ALBERT

Description: Although catchment storage is an intrinsic control on the rainfall-runoff response of streams, direct measurement remains a major challenge. Coupled models that integrate long-term hydrometric and isotope tracer data are useful tools that can provide insights into the dynamics of catchment storage and the volumes of water involved. In this study, we use a tracer-aided hydrological model to characterize catchment storage as a dynamic control on system function related to streamflow generation, which also allows direct estimation of the non-stationarity of water ages. We show that in a wet Scottish upland catchment dominated by runoff generation from riparian peats (histosols) with high water storage, non-stationarity in water age distributions are only clearly detectable during more extreme wet and dry periods. This is explained by the frequency and longevity of hydrological connectivity and the associated relative importance of flow paths contributing younger or older waters to the stream. Generally, these saturated riparian soils represent large mixing zones that buffer the time variance of water age and integrate catchment-scale partial mixing processes. Although storage simulations depend on model performance, which is influenced by input variability and the degree of isotopic damping in the stream, a longer-term storage analysis of this model indicates a system which is only sensitive to more extreme hydroclimatic variability. This article is protected by copyright. All rights reserved.

Description: Phosphorus (P) is one of the major limiting nutrient in many freshwater ecosystems. During the last decade, attention has been focused on the fluxes of suspended sediment and particulate P through freshwater drainage systems because of severe eutrophication effects in aquatic ecosystems. Hence, the analysis and prediction of phosphorus and sediment dynamics constitutes an important element for ecological conservation and restoration of freshwater ecosystems. In that sense, the development ofa suitable prediction model is justified and the present work is devoted to the validation and application of a predictive Soluble Reactive Phosphorus (SRP) uptake and sedimentation models, to a real riparian system of the middle Ebro river floodplain. Both models are coupled to a fully distributed 2D shallow water flow numerical model. The SRP uptake model is validated using data from three field experiments. The model predictions show a good accuracy for SRP concentration, where the linear regressions between measured and calculated of the three experiments were significant ( r 2  ≥ 0.62; p  ≤ 0.05), and a Nash-Sutcliffe coefficient (E) that ranged from 0.54 to 0.62. The sedimentation model is validated using field data collected during 2 real flooding events within the same river reach. The comparison between calculated and measured sediment deposition showed a significant linear regression ( p  ≤ 0.05; r 2  = 0.97) and an E that ranged from 0.63 to 0.78. Subsequently, the complete model that includes flow dynamics, solute transport, SRP uptake and sedimentation is used to simulate and analyze floodplain sediment deposition, river nutrient contribution and SRP uptake. According to this analysis, the main SRP uptake process appears to be the sediment sorption. The analysis also reveals the presence of a lateral gradient of hydrological connectivity that decreases with distance from the river, and controls the river matter contribution to the floodplain. This article is protected by copyright. All rights reserved.

Description: The inherent effects of global sea surface temperature (SST) anomalies on hydrological cycle and vegetation cover complicate the structure of tropical climate at the regional scale. Assessing hydrological processes related to climate forcing is important in Central America because it is surrounded by both the Pacific and Atlantic oceans and two continental landmasses. In this study, the use of high-resolution remote sensing imagery in wavelet analysis helps identify nonstationary characteristics of hydrological and ecological responses. The wavelet-based empirical orthogonal function (WEOF) further reflects the nonlinear relationship between the Atlantic and Pacific SST and the greenness of a pristine forested site in Panama, La Amistad International Park. Integrated WEOF and descriptive statistics for data analysis reveal a higher temporal variability in terrestrial precipitation relative to in-situ land surface temperature and its probable effects on the presence of dry periods. Such teleconnection signals of SST were identified as a driving force of decline in tropical forest greenness during dry periods. The results of our remote sensing-based wavelet analysis showed intrannual high frequency and biennial to triennial low frequency signals between enhanced vegetation index (EVI)/precipitation datasets and SST indices in both Atlantic and Pacific oceans. A spatiotemporal priority search further confirmed the importance of the effects of the El Niño-Southern Oscillation (ENSO) over terrestrial responses in the selected study site. Coincidence of the effect of ENSO teleconnection patterns on precipitation and vegetation suggest possible impacts of El Niño-associated droughts in Central America, accompanied by reduced rainfall, especially during the first months of rainy season (June, July and August), and decline in vegetation cover during the dry season (March and April). This article is protected by copyright. All rights reserved.

Description: This paper evaluates the IBIS land surface model using daily soil moisture data over a three-year period (2005–2007) at a semi-arid site in southeastern Australia, the Stanley catchment, using the Monte-Carlo GLUE approach. The model was satisfactorily calibrated for both the surface 30 cm and full profile 90 cm. However, full-profile calibration was not as good as that for the surface, which results from some deficiencies in the evapotranspiration component in IBIS. Relatively small differences in simulated soil moisture were associated with large discrepancies in the predictions of surface runoff, drainage and evapotranspiration. We conclude that while land surface schemes may be effective at simulating heat fluxes they may be ineffective for prediction of hydrology unless the soil moisture is accurately estimated. Sensitivity analyses indicated that the soil moisture simulations were most sensitive to soil parameters, and the wilting point was the most identifiable parameter. Significant interactions existed between three soils parameters: porosity, saturated hydraulic conductivity and Campbell “b” exponent so they could not be identified independent of each other. There were no significant differences in parameter sensitivity and interaction for different hydroclimatic years. Even though the data record contained a very dry year and another year with a very large rainfall event, this indicated that the soil model could be calibrated without the data needing to explore the extreme range of dry and wet conditions. IBIS was much less sensitive to vegetation parameters. The leaf area index (LAI) could affect the mean of daily soil moisture time series when LAI 〈 1, while the variance of the soil moisture time series was sensitive to LAI 〉 1. IBIS was insensitive to the Jackson rooting parameter, suggesting that the effect of the rooting depth distribution on predictions of hydrology was insignificant. This article is protected by copyright. All rights reserved.

Description: Over the past few decades ground water has become an essential commodity due to increased demand as a result of growing population, industrialization, urbanization etc. The water supply situation is expected to become more severe in the future because of continued unsustainable water use and projected change in hydro-meteorological parameters due to climate change. This study is based on the integrated approach of Remote Sensing (RS), Geographical Information System (GIS) and Multi-Criteria Decision Making (MCDM) techniques to determine the most important contributing factors that affect the ground water resources and to delineate the ground water potential zones. Ten thematic layers viz. geomorphology, geology, soil, topographic elevation (DEM), land use/land cover, drainage density, lineament density, proximity of surface water bodies, surface temperature and post-monsoon ground water depth were considered for the present study. These thematic layers were selected for ground water prospecting based on literature, discussion with the experts of Central Ground Water Board (CGWB), Government of India, field observations, geophysical investigation and multivariate techniques. The thematic layers and their features were assigned suitable weights on the Saaty's scale according to their relative significance for ground water occurrence. The assigned weights of the layers and their features were normalized by using Analytic Hierarchy Process (AHP) and eigenvector method. Finally, the selected thematic maps were integrated using weighted linear combination method to create the final ground water potential zone map. The final output map shows different zones of ground water potential, viz., very good (16%), good (35%), moderate (28%) low (17%) and very low (2.1%). The ground water potential zone map was finally validated using the discharge and ground water depth data from 28 and 98 pumping wells respectively which showed good correlation. This article is protected by copyright. All rights reserved.

Description: Bank erosion is the main source of suspended sediment (SS) and diffuse total phosphorus (TP) in many lowland catchments. This study compared a physically based sediment routing method (Physical method), which distinguishes between stream bed and bank erosion, with the original sediment routing method (Original method) within the Soil and Water Assessment Tool (SWAT) version 2009, for simulating SS and TP losses from a lowland catchment. A SWAT model was set up for the lowland River Odense catchment in Denmark and calibrated against observed stream flow and phosphate (PO 4 ) loads. Based on an initial calibration of hydrological and PO 4 parameters, the SWAT model with the Original method (Original model) and the SWAT model with the Physical method (Physical model) were calibrated separately against observed SS and TP loads. The SWAT model simulated daily stream flow well, but underestimated PO 4 loads. The Physical model simulated daily SS and TP better than the Original model. The simulated contribution of bank erosion to SS in the Physical model (99%) was close to the estimated contribution from in-situ erosion measurements (90-94%). Compared with the Original method, the Physical method is not only more conceptually correct, but also improves model performance. This article is protected by copyright. All rights reserved.

Description: This paper focuses on surface-subsurface water exchange in a steep coarse-bedded stream with step-pool morphology. We use both flume experiments and numerical modelling to investigate the influence of stream discharge, channel slope and sediment hydraulic conductivity on hyporheic exchange. The model step-pool reach, whose topography is scaled from a natural river, consists of 3 step-pool units with 0.1 m step heights, discharges ranging between base and over bankfull flows (scaled values of 0.3-4.5 L/s) and slopes of 4 and 8%. Results indicate that the deepest hyporheic flow occurs with the steeper slope and at moderate discharges and downwelling fluxes at the base of steps are highest at the largest stream discharges. In contrast to pool-riffle morphology, these findings show that steep slopes cause deeper surface-subsurface exchanges than gentle slopes. Numerical simulation results show that the portion of the hyporheic zone influenced by surface water temperature increases with sediment hydraulic conductivity. These experiments and numerical simulations emphasize the importance of topography, sediment permeability and roughness elements along the channel surface in governing the locations and magnitude of downwelling fluxes and hyporheic exchange. Our results show that hyporheic zones in these steep streams are thicker than previously expected by extending the results from streams with pool-riffle bed forms. This article is protected by copyright. All rights reserved.

Description: The objective of this analysis is to demonstrate the feasibility of using a composite L2 SMOS soil moisture product for determining drought conditions by taking advantage of its spatial and temporal resolution. The work investigates the potential relationships between soil moisture anomalies and two drought indices, the Standardized Precipitation Index (SPI) and the Standardized Precipitation Evapotranspiration Index (SPEI), both calculated on a ten-day basis. As the two drought indices can be applied to different time scales for precipitation series, the influence of time scale on the drought definition is also studied. The anomalies were calculated both for the in situ soil moisture by REMEDHUS (Soil Moisture Measurement Stations Network, Spain) and from the SMOS L2 soil moisture product. In general, in situ anomalies exhibit higher correlation coefficients for the drought indices than those of SMOS, except for the shortest time scale. As expected, the short-term remotely sensed anomalies have a high response to precipitation events. This effect may be due to the greater sensitivity of SMOS data to rainfall, as well as to the spatial averaged nature of its observations. The optimal time scale was one month for the SMOS values and ranged between 30 and 50 days for the in situ values. The use of evapotranspiration in the calculation of the indices did not improve the description of the anomalies. The relationship between indices and soil moisture conditions provides encouraging results. Indeed, this method generates preliminary but valuable insights for future satellite products. This article is protected by copyright. All rights reserved.

Description: Remote estimation of river discharge from river width variations is an intriguing method for gauging rivers without conventional measurements. Entirely cloud-free imagery of an entire river reach is often rare, but partial coverage is more frequent. Discharge is estimated from spatially discontinuous imagery via construction of multiple width-discharge rating curves within a 62 km reach of the Tanana River, Alaska. The resulting discharge error is as low as 6.7% RMSE. Imagery covering 〈20% of the study reach can be used. This article is protected by copyright. All rights reserved.

Description: Reports of abruptly declining flows of Canada's Athabasca River have prompted concern because this large, free-flowing river could be representative for northern North America, provides water for the massive Athabasca oil-sands projects, and flows to the extensive and biodiverse Peace-Athabasca, Slave and Mackenzie River deltas. To investigate historic hydrology along the river and its major tributaries we expanded the time series with interpolations for short data gaps; calculations of annual discharges from early, summer-only records; and by splicing records across sequential hydrometric gauges. These produced composite, century-long records (1913 to 2011) and trend detection with linear Pearson correlation provided similar outcomes to non-parametric Kendall τ−b tests. These revealed that the mountain and foothills reaches displayed slight increases in winter discharges versus larger declines in summer discharges, and consequently declining annual flows (~0.16%/yr at Hinton; p 〈 0.01). Conversely, with contrasting boreal contributions, the Athabasca River at Athabasca displayed no overall trend in monthly or annual flows, but there was correspondence with the Pacific Decadal Oscillation (PDO) that contributed to a temporary flow decline from 1970 to 2000. These findings from century-long records contrast with interpretations from numerous shorter-term studies, and emphasize the need for sufficient time series for hydrologic trend analyses. For Northern Hemisphere rivers, the study interval should be at least 80 years to span two PDO cycles and dampen the influence from phase transitions. Most prior trend analyses considered only a few decades and this weakens interpretations of the hydrologic consequences of climate change. This article is protected by copyright. All rights reserved.

Description: Recent studies have suggested that the hydrologic connectivity of northern headwater catchments is likely controlled by antecedent moisture conditions and land cover patterns. A water storage model ( EWS ), based on water levels ( WLs ), specific yield ( Sy ) and surface elevation ( SE ) changes was compared to a basic water budget of a small, boreal, patterned fen (13 ha) during the ice-free period. Results showed that the EWS model reproduced well storage variations derived from the water budget. These results suggest that storage variations can be properly represented by the fluctuations of WLs when we consider the heterogeneous soil properties. However, storage deviations occurred at the daily scale and could be explained by a lack of information on water retention in unsaturated layers, canopy interceptions and preferential flows. Despite the significant impact of SE changes on the different peatland cover storage budgets (strings and lawns), using Sy mean values had low impact on storage estimations. This can be explained by the large proportion of pools and high WLs throughout the fen. At the fen scale, high storage in the pools seemed to reduce the Sy difference between strings and lawns. The results of this study provide new insights about the complex hydrological behaviour of northern catchments and allow for conceiving new hydrological modeling perspectives. This article is protected by copyright. All rights reserved.

Description: Minor changes to seasonal air temperature and precipitation can have a substantial impact on the availability of water resources within large watersheds. Two such watersheds, the north-flowing Mackenzie and east-flowing Saskatchewan Basins have been identified as highly vulnerable to such changes, and, therefore, selected for study as part of the Climatic Redistribution of western Canadian Water Resources (CROCWR) project. CROCWR aims to evaluate spatial and temporal changes to water resource distribution through the analysis of a suite of hydroclimatic and streamflow variables. As part of this analysis, dominant summer (May-Oct) circulation patterns at 500-hPa for 1950-2011 are identified using the method of Self-Organizing Maps (SOM). Surface climate variables associated with these patterns are then identified, including both daily air temperature and precipitation, and seasonal Standardized Precipitation-Evapotranspiration Index (SPEI) values. Statistical methods are applied to assess the relationships between dominant circulation patterns and the Southern Oscillation Index (SOI) and Pacific Decadal Oscillation (PDO). Results indicate that mid-summer (Jul-Aug) is dominated by a split-flow blocking pattern, resulting in cool (warm), wet (dry) conditions in the southern (northern) portion of the study area. By contrast, the shoulder season (May and Oct) is dominated by a trough of low-pressure over the North Pacific Ocean. The frequency of weak split-flow blocking is higher during positive SOI and negative PDO, while ridging over the western continent is more frequent during negative SOI and positive PDO. Results from this analysis increase our knowledge of processes controlling the distribution of summer water resources in western Canada. This article is protected by copyright. All rights reserved.

Description: Little research has examined whether forests reduce stream water eutrophication in agricultural areas during spring snowmelt periods. This study evaluated the role of forests in ameliorating deteriorated stream water quality in agricultural areas, including pasture, during snowmelt periods. Temporal variation in stream water quality at a mixed land-use basin (565 ha: pasture 13%, forestry 87%), northern Japan, was monitored for 7 years. Synoptic stream water sampling was also conducted at 16 sites across a wide range of forest and agricultural areas in a basin (18.3 km 2 ) in spring, summer, and fall. Atmospheric nitrogen (N) and phosphorus (P) deposition were measured for 4 years. The results showed that concentration pulses of nitrate (NO 3 – ), organic N (ON), and total P (TP) in stream water were observed when discharge increased during spring snowmelt. Their concentrations were high when silicate concentrations were low, suggesting surface water exported from pasture largely contributed to stream water pollution during snowmelt. Atmospheric N and P deposition (4.1 kg N ha –1 y –1 ; 0.09 kg P ha –1 y –1 , respectively) was too low to affect the background concentrations of N and P in streams from forested areas. Reduction of eutrophication caused by nutrients from pasture was mainly due to dilution by water containing low concentrations of N and P exported from forested areas, while in-stream reduction were not dominant processes. Results indicate that forests have a limited capacity to reduce the concentration pulses of N and P in stream water during snowmelt in this study basin. This article is protected by copyright. All rights reserved.

Description: In NLDAS-2 Noah simulation, the NLDAS team introduced an intermediate “fix” to constrain the surface exchange coefficient when the atmospheric boundary layer is stable. In the current NLDAS-2 Noah version, this fix is used for all stable cases including snow-free grid cells. In this study, we simply apply this fix to the grid cells in which both stable atmospheric boundary layer and snow exist simultaneously, excluding the snow-free grid cells as we recognize that the fix in NLDAS-2 is too strong. We conduct a 31-year (1979-2009) NLDAS-2 Noah interim (Noah-I) run, and use observed streamflow, evapotranspiration, land surface temperature, soil temperature, and ground heat flux to evaluate the results, including comparisons with the original NLDAS-2 Noah run. The results show that Noah-I has the same performance as NLDAS-2 Noah for snow water equivalent; however, Noah-I significantly improved the simulation of other hydrometeorological products as noted above when compared to NLDAS-2 Noah and the observations. This simple modification is being included in the next Noah version used in NLDAS. The hydrometeorological products from the improved NLDAS-2 Noah-I are being staged on the NCEP public server. This article is protected by copyright. All rights reserved.

Description: Large-scale watershed modelling presents a unique challenge in terms of physiographic and climatological heterogeneity and spatially varied hydrologic responses. In particular, the spatial variability in hydrologic processes may introduce a high degree of uncertainty in the modelling of a large watershed. This study assessed the uncertainties in annual/seasonal streamflow and annual peak flow simulations with respect to selection of climate data and model parameter sets for the Variable Infiltration Capacity (VIC) model of the Athabasca River Basin (ARB) in Alberta, Canada. Two high-resolution gridded climate data sets over the 1979 to 2010 period, and six different model parameter sets calibrated corresponding to different time periods and various hydrologic patterns, were employed to quantify the uncertainty in VIC simulations. Moreover, the possibility of an ensemble approach to predict hydrologic responses in the ARB has been investigated. The results indicated that stramflow simulations near the headwater and along the Athabasca River mainsteam have high uncertainty corresponding to selection of climate data mainly due to greater difference of precipitation between the two climate data sets, whereas sub-basin stations at low-elevations were more sensitive to the selection of parameter set for interflow-dominated runoff cycle. All stations showed higher uncertainty corresponding to the selection of parameter set for annual peak flows. In addition, this study confirmed that the ensemble means can provide more accurate and consistent hydrologic information for the low-elevation area where higher internal variability exists. This article is protected by copyright. All rights reserved.

Description: Multilayer covers are widely accepted reclamation designs in the oil sands region of northern Alberta, Canada, with an ultimate goal of revegetating to species characteristic of predisturbance native plant communities. To determine the optimal depth of reclamation material required to reclaim overburden shale from an oil sands mine, an evaluation was made of the long-term performance of six reclamation soil cover depths all placed over overburden. The measured soil water contents from different cover thicknesses at South Bison Hills located at the Syncrude Mine site north of Fort McMurray, Alberta were used to calibrate and validate a dual-porosity model in HYDRUS-1D. The calibrated and validated model was then used to evaluate the influence of cover thickness and climatic variability on plant available water for forest growth. The frequency distributions of actual transpiration (T r ) for six cover treatments with a range of leaf area index (LAI) cases were developed. These T r frequency distributions were then modified by coupling T r and LAI. The modified frequency distributions for annual T r for the six simulated cover thickness highlight the strong non-linearity between the distribution of T r over a long-term (60 year) climate cycle in that incremental increases in cover thickness do not produce proportional increases in T r . The results indicated that, once the cover thickness exceeds 100 cm, there is little incremental increase in the median value of T r over the 60 year climate cycle. This article is protected by copyright. All rights reserved.

Description: Within peatland ecosystems small deviations in surface elevation result in microforms that differ in depth to water-table, plant type and rate of biogeochemical cycling, possibly leading to differences in peat physical and hydrological properties that could feed back to whole ecosystem hydrological and biogeochemical function. However, hydrological parameters for peatland microforms have not been quantified. This study determined bulk density, pore size distribution and saturated hydraulic conductivity (K sat ) at hummocks and hollows of four, Sphagnum -dominated Canadian peatlands. Study sites included both a bog and poor fen in each of Alberta and Quebec allowing for investigation of differences in peat hydrophysical properties between microforms across a range of Sphagnum -dominated peatlands. Hydraulic conductivity was determined in the laboratory on peat from the surface (0.03-0.08 m) and the saturated zone (0.20 m below the local water-table position). Peatland type, climate region, microform and depth of peat were all significant descriptors of variation in K sat . Deeper peat was less conductive than surface peat. Hummocks generally had higher K sat than hollows at both surface and saturated zones, although differences between microforms varied between sites. Differences in K sat between samples were correlated with bulk density, von Post humification and macroporosity. These results indicate that there are microtopographical differences in peat hydrophysical properties; however, the strong decline in K sat with depth indicates that differences in the local water-table, resulting in a change in depth of water flow, is likely a stronger control on local K sat than microform type. This article is protected by copyright. All rights reserved.

Description: A regional, or pooled, approach to frequency analysis is explored in the context of the estimation of rainfall quantiles required for the formation of Intensity-Duration-Frequency (IDF) curves. Resampling experiments are used, in conjunction with two rainfall data sets with long record lengths, to explore the merits of a pooled approach to the estimation of extreme rainfall quantiles. The width of the 95% confidence interval for quantile estimates is used as the primary basis to evaluate the relative merits of pooled and single site estimates of rainfall quantiles. Recommendations are formulated for applying the regional approach to frequency analysis and these recommendations are used in the application of the regional approach to 40 sites with IDF data in southern Ontario, Canada. The results demonstrate that the regional approach is preferred to single site analysis for estimating extreme rainfall quantiles for conditions and data availability commonly encountered in practice. This article is protected by copyright. All rights reserved.

Description: Integrated river basin models should provide a spatially distributed representation of basin hydrology and transport processes to allow for spatially implementing specific management and conservation measures. To accomplish this, the Soil and Water Assessment Tool (SWAT) was modified by integrating a landscape routing model to simulate water flow across discretized routing units. This paper presents a grid-based version of the SWAT landscape model that has been developed to enhance the spatial representation of hydrology and transport processes. The modified model uses a new flow separation index that considers topographic features and soil properties to capture channel and landscape flow processes related to specific landscape positions. The resulting model is spatially fully distributed and includes surface, lateral, and groundwater fluxes in each grid cell of the watershed. Furthermore it more closely represents the spatially heterogeneous distributed flow and transport processes in a watershed. The model was calibrated and validated for the Little River Watershed (LRW) near Tifton, Georgia (USA). Water balance simulations as well as 30 the spatial distribution of surface runoff, subsurface flow and evapotranspiration are examined. Model results indicate that groundwater flow is the dominant landscape process in the LRW. Results are promising and satisfactory output was obtained with the presented grid-based SWAT landscape model. Nash-Sutcliffe model efficiencies for daily stream flow were 0.59 and 0.63 for calibration and validation periods and the model reasonably simulates the impact of the landscape position on surface runoff, subsurface flow and evapotranspiration. Additional revision of the model will likely be necessary to adequately represent temporal variations of transport and flow processes in a watershed. This article is protected by copyright. All rights reserved.

Description: Direct sediment inputs from forest roads at stream crossings are a major concern for water quality and aquatic habitat. Legacy road-stream crossing approaches, or the section of road leading to the stream, may have poor water and grade control upon reopening, thus increasing the potential for negative impacts to water quality. Rainfall simulation experiments were conducted on the entire running surface area associated with six reopened stream crossing approaches in the southwestern Virginia Piedmont physiographic region, USA. Event-based surface runoff and associated total suspended solids (TSS) concentrations were compared among a succession of gravel surfacing treatments that represented increasing intensities of best management practice (BMP) implementation. The three treatments were No Gravel (10-19% cover), Low Gravel (34-60% cover), and High Gravel (50-99% cover). Increased field hydraulic conductivity was associated with maximized surface cover, and ranged from 7.2 to 41.6, 11.9 to 46.3, and 16.0 to 58.6 mm h -1 , respectively, for the No Gravel, Low Gravel, and High Gravel treatments. Median TSS concentration of surface runoff for the No Gravel treatment (2.84 g L -1 ) was greater than Low Gravel (1.10 g L -1 ) and High Gravel (0.82 g L -1 ) by factors of 2.6 and 3.5, respectively. Stream crossing approaches with 90-99% surface cover had TSS concentrations below 1 g L -1 . Reducing the length of road segments that drain directly to the stream can reduce the costs associated with gravel surfacing. This research demonstrates that judicious and low-cost BMPs can ameliorate poor water control and soil erosion associated with reopening legacy roads. This article is protected by copyright. All rights reserved.

Description: Groundwater modeling has emerged as a powerful tool to develop a sustainable management plan for efficient groundwater utilization and protection of this vital resource. This study deals with the development of five hybrid artificial neural network (ANN) models and their critical assessment for simulating spatio-temporal fluctuations of groundwater in an alluvial aquifer system. Unlike past studies, in this study, all the relevant input variables having significant influence on groundwater have been considered and the hybrid ANN technique (ANN-cum-Genetic Algorithm) has been used to simulate groundwater levels at 17 sites over the study area. The parameters of the ANN models were optimized using Genetic Algorithm (GA) optimization technique. The predictive ability of the five hybrid ANN models developed for each of the 17 sites was evaluated using six goodness-of-fit criteria and graphical indicators, together with adequate uncertainty analyses. The analysis of the results of this study revealed that the MLP-LM model is the most efficient in predicting monthly groundwater levels at almost all the 17 sites, while the RBF model is the least efficient. The GA technique was found to be superior to the commonly used trial-and-error method for determining optimal ANN architecture and internal parameters. Of the goodness-of-fit statistics used in this study, only RMSE, r 2 and NSE were found to be more powerful and useful in assessing the performance of the ANN models. It can be concluded that the hybrid ANN modeling approach can be effectively used for predicting spaio-temporal fluctuations of groundwater at basin or sub-basin scales. This article is protected by copyright. All rights reserved.

Description: Phosphorus (P) loss from agricultural watersheds has long been a critical water quality problem, the control of which has been the focus of considerable research and investment. Preventing P loss depends on accurately representing the hydrological and chemical processes governing P mobilization and transport. The Soil and Water Assessment Tool (SWAT) is a watershed model commonly used to predict runoff and non-point source pollution transport. SWAT simulates runoff employing either the curve number ( CN ) or Green and Ampt methods, both assume infiltration excess runoff, although shallow soils underlain by a restricting layer commonly generate saturation excess runoff from variable source areas (VSA). In this study, we compared traditional SWAT to a re-conceptualized version, SWAT-VSA, which represents VSA hydrology, in a complex agricultural watershed in east central Pennsylvania. The objectives of this research were to provide further evidence of SWAT-VSA's integrated and distributed predictive capabilities against measured surface runoff and stream P loads and to highlight the model's ability to drive sub-field management of P. Thus, we relied on a detailed field management database to parameterize the models. SWAT and SWAT-VSA predicted discharge similarly well (daily Nash-Sutcliffe Efficiencies of 0.61 and 0.66, respectively), but SWAT-VSA outperformed SWAT in predicting P export from the watershed. SWAT estimated lower P loss (0.0 - 0.25 kg ha -1 ) from agricultural fields than SWAT-VSA (0.0 - 1.0+ kg ha -1 ), which also identified critical source areas - those areas generating large runoff and P losses at the sub field level. These results support the use of SWAT-VSA in predicting watershed-scale P losses and identifying critical source areas of P loss in landscapes with VSA hydrology. This article is protected by copyright. All rights reserved.

Description: This article presents results of mercury in surface waters from Hunza River basin, Northern Areas, Pakistan. Small-scale gold mining activities along Hunza and Gilgit rivers are long known to be discharging mercury in the amalgamation and roasting processes. Previous studies reported high mercury concentrations in soils close to mining operations as well as serious health problems for miners. However, none of the studies have focused on the level of contamination in aqueous environments. This is the first study on the investigation of source and fate of sediment and river-borne mercury in Hunza River. Samples collected near panning sites showed higher mercury concentrations than critical levels established by the U.S. Environmental Protection Agency. The observed dissolved mercury concentrations ranged from 5.10 to 25.25 ng/L, whereas particulate-bound mercury ranged from 4.85 to 154.62 ng/L. Particulate phase mercury corresponded to more than 75% of the total observed mercury concentrations for all of the sampled rivers. Thus, suspended sediments represented the major pathway of the riverine mercury transport. A mass balance calculation suggested a 48.6 g/km 2 of annual mercury flux into Hunza River basin. The samples collected from the most affected river, Shimsal River, averaged to have 108 ng/L total mercury concentration. This number was close to the average soil mercury data from PMDC (2001) of 151 ng/L. The dominant source of contamination was shown to be the leaching of large quantities of mercury from the Hg-rich sediment and flood plain soil into the rivers rather than the direct release from mining activities. Significant decrease in both dissolved and particulate-bound mercury concentration downstream of Attabad Lake suggested that mercury is being accumulated or consumed in the lake. Although minimization or elimination of mercury loses from mining process seems important for the wellbeing of the miners, preventing remobilization of accumulated mercury is equally important in mercury control in this region. This article is protected by copyright. All rights reserved.

Description: The study of the multiannual thermal dynamics of Lake Iseo, a deep lake in the Italian pre-alpine area, is presented. Interflow was found to be the dominant river entrance mode, suggesting future susceptibility of the lake thermal structure to the overall effects of climate change expected in the upstream alpine watershed. A lake model employed the results of a long-term hydrologic model to simulate the effects of a climate change scenario on the lake's thermal evolution for the period 2012-2050. The model predicts an overall average increase in the lake water temperature of 0.012 °C/year and a reinforced Schmidt thermal stability of the water column in winter up to 800 Jm -2 . Both these effects may further prevent the deep circulation process, which is vital for the oxygenation of deep water. This article is protected by copyright. All rights reserved.

Description: Changes in water temperature can have important consequences for aquatic ecosystems, with some species being sensitive even to small shifts in temperature during some or all of their lifecycle. While many studies report increasing regional and global air temperatures, evidence of changes in river water temperature has thus far been site-specific and often from sites heavily influenced by human activities that themselves could lead to warming. Here we present a tiered assessment of changing river water temperature, covering England and Wales with data from 2,773 locations. We use novel statistical approaches to detect trends in irregularly sampled spot measurements taken between 1990 and 2006. During this 17 year period, on average, mean water temperature increased by 0.03 °C per year (± 0.002 °C) and positive changes in water temperature were observed at 2,385 (86%) sites. Examination of catchments, where there has been limited human influence on hydrological response, shows that changes in river flow have had little influence on these water temperature trends. In the absence of other systematic influences on water temperature, it is inferred that anthropogenically-driven climate change is driving some of this trend in water temperature. This article is protected by copyright. All rights reserved.

Description: Parametric method of flood frequency analysis (FFA) involves fitting of a probability distribution to the observed flood data at the site of interest. When record length at a given site is relatively longer and flood data exhibits skewness, a distribution having more than three parameters is often used in FFA such as Log Pearson Type 3 distribution. This paper examines the suitability of a 5-paramter Wakeby distribution for the annual maximum flood data in eastern Australia. We adopt a Monte Carlo simulation technique to select an appropriate plotting position formula and to derive a probability plot correlation coefficient (PPCC) test statistic for Wakeby distribution. The Weibull plotting position formula has been found to be the most appropriate for the Wakeby distribution. Regression equations for the PPCC tests statistics associated with the Wakeby distribution for different levels of significance have been derived. Furthermore, a power study to estimate the rejection rate associated with the derived PPCC test statistics has been undertaken. Finally, an application using annual maximum flood series data from 91 catchments in eastern Australia has been presented. Results show that the developed regression equations can be used with a high degree of confidence to test whether the Wakeby distribution fits the annual maximum flood series data at a given station. The methodology developed in this paper can be adapted to other probability distributions and to other study areas. This article is protected by copyright. All rights reserved.

Description: A need for more accurate flood inundation maps has recently arisen due to the increasing frequency and extremity of flood events. The accuracy of flood inundation maps is determined by the uncertainty propagated from all of the variables involved in the overall process of flood inundation modeling. Despite our advanced understanding of flood progression, it is impossible to eliminate the uncertainty due to the constraints involving cost, time, knowledge, and technology. Nevertheless, uncertainty analysis in flood inundation mapping can provide useful information for flood-risk management. The twin objectives of this study were firstly to estimate the propagated uncertainty rates of key variables in flood inundation mapping by using the first-order approximation (FOA) method and secondly to evaluate the relative sensitivities of the model variables by using the Hornberger–Spear–Young (HSY) method. Monte Carlo simulations using the Hydrologic Engineering Center's River Analysis System (HEC–RAS) and triangle-based interpolation were performed to investigate the uncertainty arising from discharge, topography, and Manning's n in the East Fork of the White River near Seymour, Indiana, and in Strouds Creek in Orange County, North Carolina. We found that the uncertainty of a single variable is propagated differently to the flood inundation area depending on the effects of other variables in the overall process. The uncertainty was linearly/nonlinearly propagated corresponding to valley shapes of the reaches. In addition, the HSY sensitivity analysis revealed the topography of Seymour reach and the discharge of Strouds Creek to be major contributors to the change of flood inundation area. This article is protected by copyright. All rights reserved.

Description: This paper provides evidence of the recovery of a small, moorland catchment to a severe drought, the most extreme on record in the UK. We present a detailed water quality time series for the post-drought recovery period, from the first significant storm event at the end of the drought through three very wet months during which time the catchment fully wetted up. High-frequency observations were obtained using pump water samplers, at 15-minute intervals for storm events and 2-hourly at other times. There are significant shifts in discharge-concentration response as the catchment wets up; initial behaviour is very different to later storms. Extreme drought may become more common in a warmer world, so it is increasingly important to understand water quality response during and after such episodes, if their impact on water resources and in-stream ecology is to be better anticipated. This article is protected by copyright. All rights reserved.

Description: Based on interactions between landscape characteristics and precipitation inputs, watersheds respond differently to different climatic inputs. The objective of this study was to quantitatively characterize controls on runoff generation from two first order micro-catchments in the Amazonia region. The study investigated the variation of hydrological signatures at micro-catchment scale, and relates these to landscape and land cover differences and weather descriptors that control the observed responses. One catchment is a pasture cleared of all natural vegetation in the early 1980's and the second catchment is a primary tropical forest with minor signs of disturbance. Water levels and meteorological variables were continuously monitored during the study period (December 2012-May 2013). Water level measurements were converted to discharge, evapotranspiration was quantified using Penman-Monteith equation and catchment pedohydrological properties were also determined. During the study period, mean total rainfall was 1200 mm and direct runoff ratios were 0.29 and 0.12 for the pasture and forest catchments, respectively. Base flow index was relatively higher in the forest catchment (0.76) compared to pasture catchment (0.63). Results from this study showed that the pasture catchment had a 35% higher mean stream flow. Analysis of selected individual rainstorm events also showed peak discharges were attained much faster in the pasture catchment compared to the forest catchment. At both sites, rainfall-runoff responses were highly dependent on surface and subsurface flow generation. Overland flow was observed in the pasture site during intense rainfall events. The pasture catchment exhibited higher event water contribution than the forest catchment. Findings from this research suggest that shallow lateral pathways play a significant role in controlling runoff generation processes in the forest catchment, while infiltration excess runoff generation processes dominate in the pasture catchment. The findings in this study suggest that the conversion of forest to pasture may lead to important changes in runoff generation processes and water storage in these head water catchments. This article is protected by copyright. All rights reserved.

Description: Changes in the water table level result in variable water saturation and variable hydrological fluxes at the interface between the unsaturated and saturated zone. This may influence the transport and fate of contaminants in the subsurface. The objective of this study was to examine the impact of a decreasing and an increasing water table on solute transport. We conducted tracer experiments at downward flow conditions in laboratory columns filled with two different uniform porous media under static and transient flow conditions either increasing or decreasing the water table. Tracer breakthrough curves were simulated using a mobile-immobile transport model. The resulting transport parameters were compared to identify dominant transport processes. Changes in the water table level affected dispersivities and mobile water fractions depending on the direction of water table movement and the grain size of the porous media. In fine glass beads the water flow velocity was similar to the decline rate of the water table and the mobile water fraction was decreased compared to steady-state saturated conditions. However, immobile water was negligible. In coarse glass beads water flow was faster due to fingered flow in the unsaturated part and the mobile water fraction was smaller than in the fine material. Here, a rising water table led to an even smaller mobile water fraction and increased solute spreading due to diffusive interaction with immobile water. We conclude that changes of the water table need to be considered to correctly simulate transport in the subsurface at the transition of the unsaturated-saturated zone. This article is protected by copyright. All rights reserved.

Description: Stemflow is an important hydrological process of rainfall partitioning, but it has rarely been studied in the alpine riparian shrub Myricaria squamosa in the Qinghai-Tibet Plateau. This study aimed to measure and model the stemflow of the unstudied M . squamosa and to identify the key controlling factors of stemflow yield. Correlations and stepwise regression analysis between stemflow and five meteorological and ten biological factors indicated that the rainfall amount and the aboveground biomass were the best variables for modeling and predicting stemflow. We used the best model to estimate annual and stand stemflow, as well as rainfall threshold for stemflow generation. Annual stemflow accounted for 2.3 to 10.2% of the annual rainfall amount, varying with different vegetation coverage and leaf area index. The annual stemflow percentage increased linearly with the annual total rainfall amount of events 〉 7.3 mm. For M . squamosa stands, branches with diameters of 10 to 25 mm were less frequent but contributed much more stemflow than branches with diameters smaller than 10 mm. The stemflow percentage increased sharply with increasing rainfall amounts when the rainfall amounts were less than 4, 8, or 13 mm for the M . squamosa stands with coverage of 32.6%, 47.6%, or 56.1%, respectively, but increased gently when the rainfall amounts were greater than these values. The rainfall threshold for stemflow generation decreased as the branch aboveground biomass increased, and the estimated median value of the rainfall threshold was 0.8 mm for M . squamosa stands, with a range of 3.0 to 0.4 mm for branches weighing 10 to 300 g, respectively. This article is protected by copyright. All rights reserved.

Description: Warming will affect snowline elevation, potentially altering the timing and magnitude of streamflow from mountain landscapes. Presently, the assessment of potential elevation-dependent responses is difficult because many gauged watersheds integrate drainage areas that are both snow- and rain-dominated. To predict the impact of snowline rise on streamflow, we mapped the current snowline (1980 m) for the Salmon River watershed (Idaho, USA) and projected its elevation after 3 °C warming (2440 m). This increase results in a 40% reduction in snow-covered area during winter months. We bolster this analysis by collecting streamflow records from a new, elevation-stratified gauging network of watersheds contained within high (2250 – 3800 m), mid (1500 – 2250 m) and low (300 – 1500 m) elevations that isolate snow, mixed, and rain-dominated precipitation regimes. Results indicate that lags between percentiles of precipitation and streamflow are much shorter in low elevations and that their annual percentiles (Q 25 & Q 75 ) of streamflow occur 30 – 50 days earlier than in mid- and high-elevation watersheds. Extreme events in low elevations are dominated by low- and no-flow events whereas mid- and high-elevations experience large magnitude floods. Only mid- and high-elevation watersheds are strongly cross-correlated with catchment-wide flow of the Salmon River, suggesting that changes in contributions from low-elevation catchments may be poorly represented using mainstem gauges. As snowline rises, mid-elevation watersheds will likely exhibit behaviors currently observed only at lower elevations. Streamflow monitoring networks designed for operational decision making or change detection may require modification to capture elevation-dependent responses of streamflow to warming. This article is protected by copyright. All rights reserved.

Description: Spatially distributed hydrological models require information on the land cover pattern, as it directly influences the generation of runoff. However, it is not clear which detail of land cover information is suitable for simulating the catchment hydrology. A better understanding of the relationship between the land cover detail and the hydrological processes is therefore required as it would enhance a successful application of the hydrological model. This study investigates the relevance of accurate information about the crop types in the catchment for the simulation of runoff, baseflow and evapotranspiration. Results reveal that adding knowledge about the crop type in the model simulation is redundant when area-averaged water flux predictions are intended. On the contrary, when a spatial distribution of water flux predictions is desired, it is meaningful to increase the land cover detail because an increased heterogeneity in the land cover map induces an increased heterogeneity in the hydrological response and locally reduces the uncertainty in the model prediction up to 50%. To assess the land cover uncertainty and to locate the regions for which the reduction in prediction uncertainty is the highest, the thematic uncertainty map (constructed through fuzzy logic) is shown to be a useful tool. This article is protected by copyright. All rights reserved.

Description: Urban streams in the northeastern United States have large road salt inputs during the winter, increased nonpoint sources of inorganic nitrogen, and decreased short-term and permanent storage of nutrients. Restoration activities that re-establish connection between streams and riparian environments may be effective for improving urban stream water quality. Meadowbrook Creek, a first-order stream in Syracuse, New York, provides a unique setting to explore impacts of stream-floodplain connection because it flows along a negative urbanization gradient, from channelized and armored headwaters to a broad, vegetated floodplain with a riparian aquifer. In this study, we investigated how reconnection to groundwater and introduction of riparian vegetation impacted urban surface water chemistry by making bi-weekly longitudinal surveys of stream water chemistry in the creek from May 2012 until June 2013. We used multiple methods to measure groundwater discharge rates along the creek. Chloride concentrations in the upstream, disconnected reach were influenced by discharge of road salt during snow melt events and ranged from 161.2 to 1440 mg/L. Chloride concentrations in the downstream, connected reach had less temporal variation, ranging from 252.0 to 1049 mg/L, due to buffering by groundwater discharge, as groundwater chloride concentrations ranged from 84.0 to 655.4 mg/L. In the summer, there was little-to-no nitrate in the disconnected reach due to limited sources and high primary productivity, but concentrations reached over 1 mg N/L in the connected reach due to the presence of riparian vegetation. During the winter, when temperatures fell below freezing, nitrate concentrations in the disconnected reach increased to 0.58 mg N/L, but were still lower than the connected reach, which averaged 0.88 mg N/L. Urban stream restoration projects that restore floodplain connection may impact water quality by storing high salinity road runoff during winter overbank events and discharging that water year-round, thereby attenuating seasonal fluctuations in chloride. Contrary to prior findings, we observed floodplain connection and riparian vegetation may alter nitrate sources and sinks such that nitrate concentrations increase longitudinally in connected urban streams. This article is protected by copyright. All rights reserved.

Description: In alluvial coastal aquifers, finer sediments are preferentially deposited along the downstream direction, so the hydraulic conductivity is generally heterogeneous and changes with distance from the coastline. To investigate the influence of aquifer heterogeneity on seawater-groundwater interaction, a new two-dimensional model characterizing groundwater flow in an aquifer-aquitard system was developed assuming that the hydraulic conductivity of the aquifer linearly increases with the distance from the coastline along the inland direction. A closed-form analytical solution was derived using the separation-of-variables method. Comparing the new solution with the numerical solution by COMSOL Multiphysics based on the finite-element method, one can see that the new solution agreed with the numerical solution very well except at the early time. We found that both aquitard leakance and the heterogeneity factor ( b ) could result in the propagation bias. The propagation bias represents the inconsistency between the theoretical calculation and the observed strong attenuation and small time lag between the head and tide fluctuations. The attenuation decreased with perpendicular distance from the coastline ( x -axis), while the time lag increased with distance along the x -axis. The relationship between the time lag and the distance along the x -axis seemed to be linear when b was 0.001m -1 , whereas it obeyed a power function when b was greater than 0.01m -1 . This article is protected by copyright. All rights reserved.

Description: Long-term heating of shallow urban aquifers is observed worldwide. Our measurements in the city of Cologne, Germany, revealed that the groundwater temperatures measured in the city center are more than 5 K higher than the undisturbed background. To explore the role of groundwater flow for the development of subsurface urban heat islands (UHIs), a numerical flow and heat transport model is set up, which describes the hydraulic conditions of Cologne and simulates the transient evolution of thermal anomalies in the urban ground. A main focus is on the influence of horizontal groundwater flow, groundwater recharge and trends in local ground warming. In order to examine heat transport in groundwater, a scenario consisting of a local hot spot with a length of 1 km of long-term ground heating was set up in the center of the city. Groundwater temperature-depth (GWTD) profiles at upstream, central and downstream locations of this hot spot are inspected. The simulation results indicate that the main thermal transport mechanisms are long-term vertical conductive heat input, horizontal advection and transverse dispersion. Groundwater recharge rates in the city are low (〈 100 mm a -1 ) and thus do not significantly contribute to heat transport into the urban aquifer. With groundwater flow, local vertical temperature profiles become very complex and are hard to interpret, if local flow conditions and heat sources are not thoroughly known. This article is protected by copyright. All rights reserved.

Description: The effect of the sample size on prediction quality is well understood. Recently studies have assessed this relationship using near continuous water quality samples. However, this is rarely possible due to financial constraints and therefore many studies have relied on simulation based methods utilising more affordable surrogates. A limitation of simulation based methods is the requirement of a good relationship, which is often not present. Therefore, catchment managers require a direct method to estimate the effect of sample size on the mean using historical water quality data. One measure of prediction quality is the precision with which a mean is estimated; this is the focus of this work. By characterising the effect of sample size on the precision of the mean, it is possible for catchment managers to adjust the sample size in relation to both the cost and the precision. Historical data is often sparse and generally collected using several different sampling schemes, all without inclusion probabilities. This means that an approach is needed to obtain unbiased estimates of the variance of the mean using a model-based approach. Using total phosphorus data from 17 subcatchments in south-eastern Australia, the ability of a model-based approach to estimate the effect of sample size on the precision of mean concentrations is examined. The effect of sample size on the precision of the mean estimate is examined for base and event-flow conditions. The effect of catchment characteristics on the precision of the mean estimates was also examined. The results showed that for estimating annual base-flow mean concentration, little gain in precision was achieved above 12 observations per year. Sample sizes greater than 12 samples per event improved event based estimates, however the inclusion of more than 12 samples per event did not greatly reduce the event mean concentration uncertainties. The precision of the base-flow estimates was most correlated to percentage urban cover while the precision of the event mean estimates was most correlated with catchment size. The method proposed in this work could be readily applied to other water quality variables, and other monitoring sites. This article is protected by copyright. All rights reserved.

Description: The U.S. Army ERDC CRREL and the USDA NRCS developed a square electronic snow water equivalent (e-SWE) sensor as an alternative to using fluid-filled snow pillows to measure SWE. The sensors consist of a center panel to measure SWE and eight outer panels to buffer edge stress concentrations. Seven 3 m square e-SWE sensors were installed in five different climate zones. During the 2011–2012 winter; 1.8 m and 1.2 m square e-SWE sensors were installed and operated in Oregon. With the exception of New York State and Newfoundland, the e-SWE sensors accurately measured SWE, with R 2 correlations between the sensor and manual SWE measurements of between 0.86 and 0.98. The e-SWE sensor at Hogg Pass, Oregon, accurately measured SWE during the past eight years of operations. In the thin, icy snow of New York during midwinter 2008–2009, the e-SWE sensors overmeasured SWE because of edge stress concentrations associated with strong icy layers and a shallow snow cover. The New York e-SWE sensors' measurement accuracy improved in spring 2009 and further improved during the 2011–2012 winter with operating experience. At Santiam Junction, measured SWE from the 1.8 m and 1.2 m e-SWE sensors agreed well with the snow pillow, 3 m e-SWE sensor, and manual SWE measurements until February 2012, when dust and gravel blew onto the testing area resulting in anomalous measurements. This article is protected by copyright. All rights reserved.

Description: For water supply, navigational, ecological protection, or water quality control purposes, there is a great need in knowing the likelihood of the river level falling below a certain threshold. Ensemble streamflow prediction (ESP) based on simulations of deterministic hydrologic models is widely used to assess this likelihood. Raw ESP results can be biased in both the ensemble means and spreads. In this study, we applied a modified Generalized Linear Model Post Processor (GLMPP) to correct these biases. The modified GLMPP is built based on regression of simulated and observed streamflow calculated based on canonical events, instead of the daily values as is done in the original GLMPP. We conducted the probabilistic analysis of post-processed ESP results falling below pre-specified low flow levels at seasonal time scale. Raw ESP forecasts from the 1980-2006 periods by four different land surface models (LSMs) in eight large river basins in the continental United States are included in the analysis. The four LSMs are Noah, Mosaic, VIC and Sacramento models. The major results from this study are: 1) a modified GLMPP was proposed based on canonical events (CE); 2) post-processing can improve the accuracy and reduce the uncertainty of hydrologic forecasts; 3) post-processing can help deal with the effect of human activity; and 4) raw simulation results from different models vary greatly in different basins. However post processing can always remove models biases under different conditions. This article is protected by copyright. All rights reserved.

Description: Stormwater along ephemeral arroyos and areal infiltration in nearby boreholes were studied in the Amargosa Desert Region of Southern Nevada, USA. Chemical composition of ephemeral stream runoff was measured at elevations below where areal infiltration generally occurs in arid environments using lysimeters designed for this study. Borehole cuttings from several wells were evaluated in terms of chloride migration. Analysis of the borehole data indicates that net areal infiltration has been insignificant for the past 10,000+ years. This is associated with an environment where chloride and other soluble salts accumulate in shallow sediments and potentially in runoff waters. Measured storm events during the four year study period were small and localized, but sufficient to produce surface runoff, at least near the lysimeters. Composition of storm runoff captured by the lysimeters was found to be a combination of the water chemistry types found in precipitation and from leaching tests of near surface sediments. All major cations and bicarbonate increased relative to chloride when precipitation interacted with sediments to form ephemeral stream runoff. The changes were consistent with calculated saturation indices. Despite the long-term accumulation of chloride in soils and deep sediments caused by complete evapotranspiration of infiltrating precipitation, runoff waters were characterized by low chloride and TDS. This study presents a limitation of the chloride mass-balance method, as chloride and water migration were disassociated from each other in the study area. This article is protected by copyright. All rights reserved.

Description: The rapid retreat of the glaciers of the Cordillera Blanca is having a noticeable impact on the downstream hydrology. Although groundwater is a critical hydrologic component that sustains stream flows during the dry season, its characteristics and its contribution to downstream hydrology remain poorly understood. In this study, we analyze the hydrochemical and isotopic properties of potential hydrologic sources mixing in surface streams to characterize the proglacial hydrology in four glacially fed watersheds within the Cordillera Blanca, Peru. Water samples from streams, glacial melt and groundwater were collected in 2008 and 2009 and analyzed for major ions and stable isotopes (δ 18 O and δ 2 H). Multivariate analysis of variance was used first to identify the hydrochemical and isotopic characteristics (tracers) of the water samples that depend primarily on the water source. Then several analyses, including hierarchical cluster analysis and mixing diagrams, were performed using these source-dependent tracers, enabling a qualitative description of the key hydrological mechanisms that characterize the study watersheds. Finally, we applied a multi-component spatial mixing model, the Hydrochemical Basin Characterization Method (HBCM), to quantify the contributions of different water sources to the outflow from the four watersheds. The HBCM results show that groundwater is a major component of the discharge during the dry season and that the groundwater contribution to outflow is greater than 24% in all of the valleys. The results are used to develop a conceptual proglacial hydrological model of the Cordillera Blanca valleys. Talus and avalanche cones are identified as key components of the hydrology of the valleys. The talus deposits collect precipitation and runoff from higher elevations (approximately 400 m above the valley floor) and have a residence time that is long enough to actively release substantial volumes of water throughout the dry season. This article is protected by copyright. All rights reserved.

Description: The solid Earth's surface frequently experience changes in total stresses due to periodic loading. When the fluid-saturated porous media deform in response to changes in stress, the induced variations in pore volume affect the pore water pressure. The fluid flow therefore occurs in response to the gradient in the induced excess pore water pressure. This work aims at quantifying the spatial variability in excess pressure head produced by the periodic loading accounting for the variation of log hydraulic conductivity (ln K ). It is important for the rational management of groundwater resources. A closed-form expression is developed by the nonstationary spectral approach to analyze the influence of the statistical properties of ln K process, the hydraulic parameters, and the spatial position. The general stochastic framework outlined in this work provides a basis for assessing the impact of statistical properties of input aquifer parameters on the output variability (or uncertainty). This article is protected by copyright. All rights reserved.

Description: Lacustrine groundwater discharge (LGD) transports nutrients from catchment to lake, which may fuel eutrophication, one of the major threats to our fresh waters. Unfortunately, LGD has often been disregarded in lake nutrient studies. Most measurement techniques are based on separate determinations of volume and nutrient concentration of LGD: Loads are calculated by multiplying seepage volumes by concentrations of exfiltrating water. Typically low phosphorus (P) concentrations of pristine groundwater often are increased due to anthropogenic sources such as fertilizer, manure or sewage. Mineralization of naturally present organic matter might also increase groundwater P. Reducing redox conditions favour P transport through the aquifer to the reactive aquifer-lake interface. In some cases, large decreases of P concentrations may occur at the interface, e. g., due to increased oxygen availability, while in other cases there is nearly no decrease in P. The high reactivity of the interface complicates quantification of groundwater-borne P loads to the lake, making difficult clear differentiation of internal and external P loads to surface water. Anthropogenic sources of nitrogen (N) in groundwater are similar to those of phosphate. However, the environmental fate of N differs fundamentally from P because N occurs in several different redox states, each with different mobility. While nitrate behaves essentially conservatively in most oxic aquifers, ammonium's mobility is similar to that of phosphate. Nitrate may be transformed to gaseous N 2 in reducing conditions and permanently removed from the system. Biogeochemical turnover of N is common at the reactive aquifer-lake interface. Nutrient loads from LGD were compiled from the literature. Groundwater-borne P loads vary from 0.74 to 2,900 mg PO 4 -P m -2  yr -1 ; for N, these loads vary from 0.001 to 640 g m -2  yr -1 . Even small amounts of seepage can carry large nutrient loads due to often high nutrient concentrations in groundwater. Large spatial heterogeneity, uncertain areal extent of the interface, and difficult accessibility make every determination of LGD a challenge. However, determinations of LGD are essential to effective lake management. This article is protected by copyright. All rights reserved.

Description: Rainfall data is a fundamental input for effective planning, design and operation of water resources projects. A well-designed rain gauge network is capable of providing accurate estimates of necessary areal average and/or point rainfall estimates at any desired ungauged location in a catchment. Increasing network density with additional rain gauge stations has been the main underlying criterion in the past to reduce error and uncertainty in rainfall estimates. However, installing and operation of additional stations in a network involves large cost and manpower. Hence, the objective of this study is to design an optimal rain gauge network in the Middle Yarra River catchment in Victoria, Australia. The optimal positioning of additional stations as well as optimally relocating of existing redundant stations using the kriging-based geostatistical approach was undertaken in this study. Reduction of kriging error was considered as an indicator for optimal spatial positioning of the stations. Daily rainfall records of 1997 (an El Niño year) and 2010 (a La Niña year) were used for the analysis. Ordinary kriging was applied for rainfall data interpolation to estimate the kriging error for the network. The results indicate that significant reduction in the kriging error can be achieved by the optimal spatial positioning of the additional as well as redundant stations. Thus, the obtained optimal rain gauge network is expected to be appropriate for providing high quality rainfall estimates over the catchment. The concept proposed in this study for optimal rain gauge network design through combined use of additional and redundant stations together is equally applicable to any other catchment. This article is protected by copyright. All rights reserved.

Description: The temporal variability in nitrogen (N) transport in the Corbeira agroforestry catchment (NW Spain) was analyzed from October 2004 to September 2008. Nitrate (NO 3 -N) and total Kjeldahl nitrogen (TKN) loads and concentrations were determined at various time scales (annual, seasonal and event). The results revealed a strong intra- and inter-annual variability in N transport influenced by weather patterns, and consequently by the hydrological regime. Mean annual export of total N in the catchment was 5.5 kg ha -1  yr -1 , with NO 3 -N being the dominant form. Runoff events comprised 10% of the study period, but contributed 40% and 61% of the total NO 3 -N and TKN loads, respectively. The NO 3 -N and TKN concentrations were higher during runoff events than under baseflow conditions, pointing to diffuse sources of N. The mobilization of TKN during runoff events was attributed to surface runoff, while NO 3 -N might be related to subsurface and groundwater flow. Runoff events were characterized by high variability in N loads and concentrations. Higher variability was observed in N loads than in N concentrations, indicating that event magnitude plays an important role in N transport in this catchment; event magnitude explained approximately 96% of the NO 3 -N load. However, a combination of variables related to runoff-event intensity (rainfall, discharge increase and kinetic energy) explained only 66% of the TKN load. This article is protected by copyright. All rights reserved.

Description: A Bayesian Chemical Mass Balance (CMB) approach was used to assess the contribution of potential sources for fluvial samples from Laurel Hill Creek in southwest Pennsylvania. The Bayesian approach provides the joint probability density functions of the sources’ contributions considering the uncertainties due to source and fluvial sample heterogeneity and measurement error. Both elemental profiles of sources and fluvial samples and 13 C and 15  N isotopes were used for the source apportionment. The sources considered include stream bank erosion, forest, roads and agriculture (pasture and cropland). Agriculture was found to have the largest contribution, followed by stream bank erosion. Also, road erosion was found to have a significant contribution in three of the samples collected during lower intensity rain events. The source apportionment was performed with and without isotopes. The results were largely consistent, however, the use of isotopes was found to slightly increase the uncertainty in most of the cases. The correlation analysis between the contributions of sources shows strong correlations between stream bank and agriculture whereas roads and forest seem to be less correlated to other sources. Thus the method was better able to estimate roads and forest contributions independently. The hypothesis that the contributions of sources are not seasonally changing was tested by assuming that all ten fluvial samples had the same source contributions. This hypothesis was rejected, demonstrating a significant seasonal variation in the sources of sediments in the stream. This article is protected by copyright. All rights reserved.

Description: We analyze the groundwater level changes following the Wenchuan earthquake in three wells – NX, DZ, and BBLY – located in the same fault zone, in the near field (distance of ~300 km from the epicenter). Co-seismic falls in the water level and gradual recovery were recorded in these wells but with different recovery periods (from 200 days to more than 1600 days). The response of the groundwater level to Earth tides is used as a proxy to explore the permeability evolution. We found that the permeability increased in response to the Wenchuan earthquake in the three wells but with different post-earthquake recovery processes. Only BBLY recovered to its pre-earthquake value and remained stable 260 days after the Wenchuan earthquake. The permeability in NX returned to its pre-earthquake value over a similar period but then continued to drop. The permeability in DZ returned to its pre-earthquake value much quicker than that in the other two wells, and remained stable below the pre-earthquake value 200 days after the earthquake. This suggests that the groundwater level changes in the three wells were caused mainly by permeability changes. In the BBLY well, the unclogging/clogging of the fracture flow path mechanism may explain the permeability evolution, while mechanisms such as unclogging/clogging or the opening/closing of the fracture associated with blocking of the narrow fracture apertures appears to be responsible for the permeability evolution in the NX and DZ wells. This article is protected by copyright. All rights reserved.

Description: The major goals of this study were to determine stream bed sediment erosion/deposition rates, sediment age, percent “new” sediment, and suspended sediment origin during two storm events of contrasting magnitudes (11.9 mm over 5 h and 58.9 mm over 39 h) using fallout radionuclides (excess lead 210 - 210 Pb xs and beryllium 7 - 7 Be) and link the nature and type of sediment source contributions to potential phosphorus (P) off-site transport. The study was conducted in cropland-dominated and mixed-land-use subwatersheds in the non-glaciated Pleasant Valley watershed (50 km 2 ) in South Central Wisconsin. Fine sediment deposition and erosion rates on stream beds varied from 0.76 to 119.29 mg cm -2 d -1 (at sites near the watershed outlet) and 1.72 to 7.72 mg cm -2 d -1 (at sites in the headwaters), respectively, during the two storm events. The suspended sediment age ranged from 123 ± 12 days to 234 ± 33 days during the smaller storm event; however, older sediment was more prevalent (p =0.037) in the streams during the larger event with suspended sediment age ranging from 226 ± 9 days to 322 ± 114 days. During the small and large storm event, percent “new” sediment in suspended sediment ranged from 5.3 ± 2.1% to 21.0 ± 2.9% and 5.3 ± 2.7% to 6.7 ± 5.7%, respectively. In the cropland dominated subwatershed, upland soils were the major source of suspended sediment, whereas in the mixed land use subwatershed, both uplands and stream banks had relatively similar contributions to suspended sediment. In-stream (suspended and bed) sediment P levels ranged from 703 ± 193 to 963 ± 84 mg kg -1 during the two storm events. The P concentrations in suspended and bed sediment were reflective of the dominant sediment source (upland or stream bank or mixed). Overall, sediment transport dynamics showed significant variability between subwatersheds of different land use characteristics during two contrasting storm events. This article is protected by copyright. All rights reserved.

Description: When " fingerprinting" is used to identify what proportions P s ( s  =  1 … g ) of suspended sediment come from g different source areas, measures of the uncertainties in estimates of the P s are also required. These uncertainties are influenced by two kinds of correlation whose effects are rarely recognized in the literature. These are (i) correlation between the estimated P s because they must add to one, and (ii) correlation between the geochemical tracers measured in sediment samples. This paper uses bootstrap procedures to identify joint confidence regions for the estimated proportions (responding to correlation of type (i)) and to explore alternatives to the " Standard" least-squares criterion used to estimate the proportions when tracer measurements are correlated (correlation of type (ii)). Using a limited data-set with three sediment source areas for illustration ( g  =  3 ), results were obtained from 5000 bootstrap samples, using two criteria (Standard and Generalized Least Squares, GLS) with two inequality constraints (a) 0  ≤  P s ≤ 1 , where P s is the fraction of suspended sediment contributed by the s -th source area ( s  =  1 , 2 , 3 ); (b) 0  〈  P s 〈 1 which, the paper argues, better represents reality. Approximate 95% confidence regions for the P s , given by the two criteria and two inequality constraints, were compared. Using the inequality constraints (a), the confidence region given by the GLS criterion was slightly smaller than that given by the Standard; using the constraints (b), the two confidence regions' boundaries were almost identical, suggesting that the effects of correlations between tracers was not large for the data-set used. For both criteria, the scatter amongst estimated proportions P s obtained by boot-strapping was large, raising issues concerning the efficiency of sampling and the allocation of sampling effort, both in source areas and in transported suspended sediment. The results suggest that apparently small differences in the constraints applied to the proportions P s can give quite different numerical results. This article is protected by copyright. All rights reserved.

Description: In this study, the Hillslope River Routing (HRR) model was modified for arctic river basin applications and used to route surface and subsurface runoff from the Community Land Model (CLM) in the Mackenzie River Basin (MRB) for the period 2000-2004. The HRR modeling framework performs lateral surface and subsurface runoff routing from hillslopes and channel/floodplain routing. The HRR model was modified here to include a variable subsurface Active Layer Thickness (ALT; permafrost) to enable subsurface water to re-surface, a distributed surface storage component to store and attenuate the rapid generation of snowmelt water, compound hillslopes to account for the low relief near rivers and floodplains, and reservoir routing to complete the total surface and subsurface water storage accounting. To illustrate the new HRR model components, a case study is presented for the MRB. The basin is discretized into 5,077 sub-basins based on a drainage network derived from the global Digital Elevation Model (DEM) developed from the ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer) sensor on board NASA's Terra satellite and river widths extracted from LandSat images. The median hillslope land area is 68.5 km 2 with a flow length of 2.8 km. Gridded CLM surface and subsurface runoffs are re-mapped to the HRR model's irregular sub-basins. The role of each new model component is quantified in terms of peak annual streamflow (magnitude and timing) at select locations and basin-wide total water storage anomalies. The role of distributed surface storage is shown to attenuate the relatively rapid generation of snowmelt water, impact the annual peak hydrograph (reduced peaks by 〉30% and detailed peak by 〉20 days) and account for 20% of the monthly total water storage anomalies averaged over the year and ranging from 14 to 25% (-10 to 30 mm) throughout the year. Although additional research is needed to dynamically link spatially distributed ALT to HRR, the role of ALT is shown to be important. A basin-wide, uniform 1 m ALT impacts the annual peak hydrograph (reduced peaks by 9% and detailed peak by 8 days) and trends in total water storage anomalies. This article is protected by copyright. All rights reserved.

Description: The synthesis of experimental understanding of catchment behaviour and its translation into qualitative perceptual models is an important objective of hydrological sciences. We explore this challenge by examining the cumulative understanding of the hydrology of three experimental catchments and how it evolves through the application of different investigation techniques. The case study considers the Huewelerbach, Weierbach and Wollefsbach headwater catchments of the Attert basin in Luxembourg. Subsurface investigations including bore holes and pits, analysis of soil samples and Electrical Resistivity Tomography measurements are presented and discussed. Streamflow and tracer data are used to gain further insights into the streamflow dynamics of the catchments, using end-member mixing analysis and hydrograph separation based on dissolved silica and electrical conductivity. We show that the streamflow generating processes in all three catchments are controlled primarily by the subsolum and underlying bedrock. In the Huewelerbach, the permeable sandstone formation supports a stable groundwater component with little seasonality, which reaches the stream through a series of sources at the contact zone with the impermeable marls formation. In the Weierbach, the schist formation is relatively impermeable and supports a “fill and spill”-type of flow mechanism; during wet conditions, it produces a delayed response dominated by pre-event water. In the Wollefsbach, the impermeable marls formation is responsible for a saturation-excess runoff generating process, producing a fast and highly seasonal response dominated by event water. The distinct streamflow generating processes of the three catchments are represented qualitatively using perceptual models. The perceptual models are in turn translated into quantitative conceptual models, which simulate the hydrological processes using networks of connected reservoirs and transfer functions. More generally, the paper illustrates the evolution of perceptual models based on experimental fieldwork data, the translation of perceptual models into conceptual models, and the value of different types of data for processes understanding and model representation. This article is protected by copyright. All rights reserved.

Description: The Tarim River Basin (TRB) is a special endorheic arid drainage basin in Central Asia, characterized by limited rainfall and high evaporation as common in deserts, while water is supplied mainly by glacier and snow melt from the surrounding mountains. The existing drought indices can hardly capture the drought features in this region as droughts are caused by two dominant factors (meteorological and hydrological conditions). To overcome the problem, a new hybrid drought index (HDI), integrating the meteorological and hydrological drought regimes, was developed and tested in the basin in the work. The index succeeded in revealing the drought characteristics and the ensemble influence better than the single standardized precipitation index (SPI) or the hydrological index (HI). The Artificial Neural Network approach based on temperature and precipitation observations was set up to simulate the HDI change. The method enabled constructing scenarios of future droughts in the region using climate simulation of the GCMs under four RCP scenarios from the latest CMIP5 project. The simulations in the study have shown that the water budget patterns in the Tarim River Basin are more sensitive to temperature than to precipitation. Dominated by temperature rise causing an accelerating snow/glacier melt, the frequency of drought months is projected to decrease by about 14% in the next decades (until 2035). The drought duration is expected to be shortened to 3 months on average, with the severity alleviated. However, the region would still suffer more severe droughts with a high intensity in some years. The general decrease in drought frequency and intensity over the region in future would be beneficial for water resources management and agriculture development in the oases. This article is protected by copyright. All rights reserved.

Description: Temporal and spatial variations of stable oxygen ( 18 O) and hydrogen ( 2 H) isotope measurements in precipitation act as important proxies for changing hydro-meteorological and regional and global climate patterns. Temporal trends in time series of the stable isotope composition in precipitation were rarely observed and they are poorly understood. These might be a result of a lack of proper trend detection tools and effort for exploring trend processes. Here we investigate temporal trends of δ 18 O in precipitation at 17 observation station in Germany between 1978 and 2009. We test if significant trends in the isotope time series from different models can be observed. Mann-Kendall trend tests are applied on the isotope series, using general multiplicative seasonal autoregressive integrate moving average (ARIMA) models which account for first and higher order serial correlations. Effects of temperature, precipitation, and geographic parameters on isotope trends are also investigated in the proposed models. To benchmark our proposed approach, the ARIMA results are compared to a trend-free prewhiting (TFPW) procedure, the state of the art method for removing the first order autocorrelation in environmental trend studies. Moreover, we further explore whether higher order serial correlations in isotope series affects our trend results. Overall, three out of the 17 stations show significant changes when higher order autocorrelation are adjusted, and four show a significant trend when temperature and precipitation effects are considered. The significant trends in the isotope time series generally occur only at low elevation stations. Higher order autoregressive processes are shown to be important in the isotope time series analysis. Results suggest that the widely used trend analysis with only the first order autocorrelation adjustment may not adequately take account of the high order autocorrelated processes in the stable isotope series. The investigated time series analysis method including higher autocorrelation and external climate variable adjustments is shown to be a better alternative. This article is protected by copyright. All rights reserved.

Description: Runoff generation and soil loss from slopes have been studied for decades, but the relationships among runoff, soil loss, and rill development are still not well understood. In this paper, rainfall simulation experiments were conducted in two neighboring plots (scale: 1 m by 5 m) with four varying slopes (17.6%, 26.8%, 36.4% and 46.6%) and two rainfall intensities (90 mm h -1 and 120 mm h -1 ) using two loess soils. Data on rill development were extracted from the digital elevation models (DEMs) by means of photogrammetry. The effects of rainfall intensity and slope gradient on runoff, soil loss, and rill development were different for the two soils. The runoff and soil loss from the Anthrosol surface were generally higher than those from the Calcaric Cambisol surface. Higher rainfall intensity produced less runoff and more sediment for almost each treatment. With increasing slope gradient, the values of cumulative runoff and soil loss peaked, except for the treatments with 90 mm h -1 rainfall on the slopes with Anthrosol. With rainfall duration, runoff discharge decreased for Anthrosol and increased for Calcaric Cambisol for almost all the treatments. For both soils, sediment concentration was very high at the onset of rainfall and decreased quickly. Almost all the sediment concentrations increased on the 17.6% and 26.8% slopes and peaked on the 36.4% and 46.6% slopes. Sediment concentrations were higher on the Anthrosol slopes than on the Calcaric Cambisol slopes. At 90 mm h -1 rainfall intensity, increasingly denser rills appeared on the Anthrosol slope as the slope gradient increased, while only steep slopes (36.4% and 46.6%) developed rills for the Calcaric Cambisol soil. The contributions of rill erosion ranged from 36% to 62% of the cumulative soil losses for Anthrosol, while the maximum contribution of rill erosion to the cumulative soil loss was only 37.9% for Calcaric Cambisol. This article is protected by copyright. All rights reserved.

Description: Hydro-climatic impacts in water resources systems are typically assessed by forcing a hydrologic model with outputs from general circulation models (GCMs) or regional climate models (RCMs). Challenges of this approach include maintaining a consistent energy budget between climate and hydrologic models and also properly calibrating and verifying the hydrologic models. Subjective choices of loss, flow routing, snowmelt and evapotranspiration (ET) computation methods also increase watershed modeling uncertainty and thus complicate impact assessment. An alternative approach, particularly appealing for ungauged basins or locations where record lengths are short, is to predict selected streamflow quantiles directly from meteorological variables output from climate models using regional regression models that also include physical basin characteristics. In this study, regional regression models are developed for the western Great Lakes states using ordinary least squares (OLS) and weighted least squares (WLS) techniques applied to selected Great Lakes watersheds. Model inputs include readily available downscaled GCM outputs from the Coupled Model Inter-comparison Project phase 3 (CMIP3). The model results provide insights to potential model weaknesses, including comparatively low runoff predictions from continous simulation models that estimate potential evapotranspiration (PET) using temperature proxy information, and comparatively high runoff projections from regression models that do not include temperature as an explanatory variable. This article is protected by copyright. All rights reserved.

Description: Water Cloud Model (WCM) relates the backscatter coefficient (σ o ) with soil moisture. The backscatter coefficient includes the backscatter coefficient due to vegetation (σ o veg ), and the backscatter coefficient due to soil (σ o soil ). The σ o veg of WCM depends upon vegetation characteristics. The present study is aimed to investigate the effect of different vegetation descriptors in estimating soil moisture from WCM. The study is carried out in Solani river catchment of India. ENVISAT ASAR images of three dates were acquired for the study. The field data, volumetric soil moisture from the upper 0-10 cm soil layer, soil texture, soil surface roughness, Leaf Area Index (LAI), Leaf Water Area Index (LWAI), Normalized Plant Water Content (NPWC) and average Plant Height (PH) corresponding to satellite pass dates were collected. Genetic Algorithm optimization technique is used to estimate the WCM vegetation parameters. The use of LAI as vegetation descriptor results in minimum root mean square error (RMSE) of 1.77 dB between WCM computed backscatter and ENVISAT ASAR observed backscatter. Also, use of LAI in WCM as vegetation descriptor results in the least RMSE of 4.19%, between estimated and observed soil moisture for the first field campaign while it was 5.64% for the last field campaign which was undertaken after 35 days of first campaign. It is concluded that LAI can be treated as the best vegetation descriptor in studies retrieving soil moisture and backscatter from microwave remote sensing data. This article is protected by copyright. All rights reserved.

Description: Irrigation of agricultural oases is the main water consumer in semi-arid and arid regions of Northwestern China. The accurate estimation of evapotranspiration (ET) on the oases is extremely important for evaluating water use efficiency so as to reasonably allocate water resources, particularly in semi-arid and arid areas. In this study we integrated the soil moisture information into SEBS for improving irrigated crop water consumption estimation. The new approach fed with the MODIS images mapped spatiotemporal ET on the oasis in the middle reach of the Heihe river. The daily evapotranspiration (ET daily ) outputs of the new approach were compared with that of the original SEBS using the eddy correlation (EC) observations, and the results demonstrates that the modified SEBS remedied the shortcoming of general overestimating ET without regard to soil water stress. Meanwhile, the crop planting structure and LAI spatiotemporal distribution in the studied region were derived from the high resolution Chinese satellite HJ-1/CCD images for helping analyse the pattern of the monthly evapotranspiration (ET monthly ). The results show that the spatiotemporal variation of ET monthly is closely related to artificial irrigation and crop growth. Further evaluation of current irrigation water use efficiency were conducted on both irrigation district scale and the whole middle reach of the Heihe river. The results reveal that the average fraction of consumed water on irrigation district scale is 57% in 2012. The current irrigation water system is irrational because only 52 % of the total irrigated amount was used to fulfill plant evapotranspiration requirement and the rest of the irrigation water recharged into groundwater in the oasis in 2012. However, in view of the whole middle reach of the Heihe river, the irrigation water use efficiency could reach to 66% in 2012. But pumping groundwater for reused irrigation wastes mostly energy instead of water. An improved irrigation water allocation system according to actual ET requirement is needed to increase irrigation efficiency/per m 3 water resource in an effort to save both water and energy. This article is protected by copyright. All rights reserved.

Description: The current generation of catchment travel time distribution (TTD) research, integrating nearly three decades of work since publication of Water's Journey from Rain to Stream (Grip and Rodhe, 1994), seeks to represent the full distribution in catchment travel times and its temporal variability. Here, we compare conceptualizations of increasing complexity with regards to mixing of water storages and evaluate how these assumptions influence time-variable TTD estimates for two catchments with contrasting climates: the Gårdsjön catchment in Sweden and the Marshall Gulch catchment in Arizona, USA. Our results highlight that, as long as catchment TTDs cannot be measured directly but need to be inferred from input-output signals of catchments, the inferred catchment TTDs depend strongly on the underlying assumptions of mixing within a catchment. Furthermore, we found that the conceptualization of the evapotranspiration flux strongly influences the inferred travel times of stream discharge. For the wet and forested Gårdsjön catchment in Sweden, we inferred that evapotranspiration most likely resembles a completely mixed sample of the water stored in the catchment; however, for the drier Marshall Gulch catchment in Arizona, evapotranspiration predominantly contained the younger water stored in the catchment. For the Marshall Gulch catchment, this higher probability for young water in evapotranspiration resulted in older water in the stream compared to travel times inferred with assumptions of complete mixing. New observations that focus on the TTD of the evapotranspiration flux and the actual travel time of water through a catchment are necessary to improve identification of mixing and consequently travel times of stream water. This article is protected by copyright. All rights reserved.

Description: Exceptional rainfall events cause significant losses of soil, although few studies have addressed the validation of model predictions at field scale during severe erosive episodes. In this study we evaluate the predictive ability of the enhanced Soil Erosion and Redistribution Tool ( SERT-2014 ) model for mapping and quantifying soil erosion during the exceptional rainfall event (ca. 235 mm) that affected the Central Spanish Pyrenees in October 2012. The capacity of the simulation model is evaluated in a fallow cereal field (1.9 ha) at a high spatial scale (1 x 1 meter). Validation was performed with field-quantified rates of soil loss in the rills and ephemeral gullies and also with a detailed map of soil redistribution. The SERT-2014 model was run for the six rainfall sub-events that made up the exceptional event, simulating the different hydrological responses of soils with maximum runoff depths ranging between 40 and 1017 mm. Predicted average and maximum soil erosion was 11 and 117 Mg ha −1 event −1 , respectively. Total soil loss and sediment yield to the La Reina gully amounted to 16.3 and 9.0 Mg event −1 . These rates are in agreement with field estimations of soil loss of 20.0 Mg event −1 . Most soil loss (86%) occurred during the first sub-event. Although soil accumulation was overestimated in the first sub-event due to the large amount of detached soil, the enhanced SERT-2014 model successfully predicted the different spatial patterns and values of soil redistribution for each sub-event. Further research should focus on stream transport capacity. This article is protected by copyright. All rights reserved.

Description: This work examines future flood risk within the context of integrated climate and hydrologic modeling uncertainty. The research questions investigated are 1) whether hydrologic uncertainties are a significant source of uncertainty relative to other sources such as climate variability and change, and 2) whether a statistical characterization of uncertainty from a lumped, conceptual hydrologic model is sufficient to account for hydrologic uncertainties in the modeling process. To investigate these questions, an ensemble of climate simulations are propagated through hydrologic models and then through a reservoir simulation model to delimit the range of flood protection under a wide array of climate conditions. Uncertainty in mean climate changes and internal climate variability are framed using a risk-based methodology and are explored using a stochastic weather generator. To account for hydrologic uncertainty, two hydrologic models are considered, a conceptual, lumped parameter model and a distributed, physically-based model. In the conceptual model, parameter and residual error uncertainties are quantified and propagated through the analysis using a Bayesian modeling framework. The approach is demonstrated in a case study for the Coralville Dam on the Iowa River, where recent, intense flooding has raised questions about potential impacts of climate change on flood protection adequacy. Results indicate that the uncertainty surrounding future flood risk from hydrologic modeling and internal climate variability can be of the same order of magnitude as climate change. Furthermore, statistical uncertainty in the conceptual hydrological model can capture the primary structural differences that emerge in flood damage estimates between the two hydrologic models. This article is protected by copyright. All rights reserved.

Description: The traditional hydrological time series methods tend to focus on the mean of whichever variable is analyzed, but neglect its time-varying variance (i.e. assuming the variance remains constant). The variances of hydrological time series vary with time under anthropogenic influence. There is evidence that extensive well drilling and groundwater pumping can intercept groundwater runoff, and consequently induce spring discharge volatility or variance varying with time (i.e. heteroskedasticity). To investigate the time-varying variance or heteroskedasticity of spring discharge, this paper presents a seasonal autoregressive integrated moving average with general autoregressive conditional heteroskedasticity (SARIMA-GARCH) model, whose the SARIMA model is used to estimate the mean of hydrological time series, and the GARCH model estimates its time-varying variance. The SARIMA-GARCH model was then applied to the Xin'an Springs Basin, China, where extensive groundwater development has occurred since 1978 (e.g. the average annual groundwater pumping rates were less than 0.20 m 3 /s in the 1970s, reached 1.20 m 3 /s at the end of the 1980s, surpassed 2.0 m 3 /s in the 1990s, and exceeded 3.0 m 3 /s by 2007). To identify whether human activities or natural stressors caused the heteroskedasticity of Xin'an Springs discharge, we segmented the spring discharge sequence into two time periods: a predevelopment stage (i.e. 1956-1977) and a developed stage (i.e. 1978-2012), and set up the SARIMA-GARCH model for the two stages, respectively. By comparing the models, we detected the role of human activities in spring discharge volatility. The results showed that human activities caused the heteroskedasticity of the Xin'an Spring discharge. The predicted Xin'an Springs discharge by the SARIMA-GARCH model showed that the mean monthly spring discharge is predicted to continue to decline to 0.93 m 3 /s in 2013, 0.67 m 3 /s in 2014, and 0.73 m 3 /s in 2015. This article is protected by copyright. All rights reserved.

Description: The impact of global climate change on runoff components, especially on the type of overland flow, is of utmost significance. High-resolution temporal rainfall plays an important role in determining the hydrological response of quick runoff components. However, hydrological climate change scenario analyses with high temporal resolution are rare. This study investigates the impact of climate change on discharge peak events generated by rainfall, snowmelt, and soil-frost induced runoff using high-resolution hydrological modelling. The study area is Schäfertal catchment (1.44 km 2 ) in the lower Harz Mountains in central Germany. The WaSiM-ETH hydrological model is used to investigate the rainfall response of runoff components under near future (2021-2050) and far-distant future (2071-2100) climatic conditions. Disaggregated daily climate variables of WETTREG2010 SRES scenario A1B are used on a temporal resolution of 10-minute. Hydrological model parameter optimization and uncertainty analysis was conducted using the Differential Evolution Adaptive Metropolis (DREAM_(ZS)) uncertainty tool. The scenario results show that total runoff and interflow will increase by 30% and 29% in the near future and decrease by 15.9% and 14% in the far-distant future compared to the baseline scenario. In contrast, overland flow and the number and size of peak runoff will decrease moderately for the near future and drastically for the far-distant future compared to the baseline scenario. We found the strongest decrease for soil-frost induced discharge peaks at 79.6% in the near future and at 98.2% in the far-distant future scenario. It can be concluded that high-resolution hydrological modelling can provide detailed predictions of future hydrological regimes and discharge peak events of the catchment. Copyright © 2014 John Wiley & Sons, Ltd.

Description: Spatial information on soil properties is an important input to hydrological models. In current hydrological modeling practices, soil property information is often derived from soil category maps by the linking method in which a representative soil property value is linked to each soil polygon. Limited by the area-class nature of soil category maps, the derived soil property variation is discontinuous and less detailed than high resolution digital terrain or remote sensing data. This research proposed dmSoil , a data-mining-based approach to derive continuous and spatially detailed soil property information from soil category maps. First, the soil-environment relationships are extracted through data mining of a soil map. The similarity of the soil at each location to different soil types in the soil map is then estimated using the mined relationships. Prediction of soil property values at each location is made by combining the similarities of the soil at that location to different soil types and the representative soil property values of these soil types. The new approach was applied in the Raffelson Watershed and Pleasant Valley in the Driftless Area of Wisconsin, United States to map soil A horizon texture (in both areas) and depth to soil C horizon (in Pleasant Valley). The property maps from the dmSoil approach capture the spatial gradation and details of soil properties better than those from the linking method. The new approach also shows consistent accuracy improvement at validation points. In addition to the improved performances, the inputs for the dmSoil approach are easy to prepare and the approach itself is simple to deploy. It provides an effective way to derive better soil property information from soil category maps for hydrological modelling. Copyright © 2014 John Wiley & Sons, Ltd.

Description: The Green-Ampt infiltration equation is an incomplete governing equation for rainfall infiltration due to the absence of an inertia term. The estimation of the capillary pressure head at the wetting front is difficult to determine. Thus, a major limitation of the Green-Ampt model is the constant, non-zero surface ponding depth. This paper proposes an integrated rainfall infiltration model based on the Green-Ampt model and the SCS-CN model. It achieves a complete governing equation for rainfall infiltration by momentum balance and the water budget based on the Green-Ampt assumption, and uses the curve number from the SCS-CN method to calculate the initial abstraction, which is used as a basic parameter for the governing equation of the intensity of rainfall loss during the runoff period. The integrated rainfall infiltration model resolves the dilemma for capillary pressure head estimation, overcomes the limitation of constant, non-zero surface ponding depth, and facilitates the calculation of runoff for individual flood simulations. Copyright © 2014 John Wiley & Sons, Ltd.

Description: Spreading-basin methods have resulted in more than 130 million cubic meters of recharge to the unconfined Navajo Sandstone of southern Utah in the past decade, but infiltration rates have slowed in recent years because of reduced hydraulic gradients and clogging. Trench infiltration is a promising alternative technique for increasing recharge and minimizing evaporation. This paper uses a variably saturated flow model to further investigate the relative importance of the following variables on rates of trench infiltration to unconfined aquifers: saturated hydraulic conductivity, trench spacing and dimensions, initial water-table depth, alternate wet/dry periods, and number of parallel trenches. Modeling results showed (1) increased infiltration with higher hydraulic conductivity, deeper initial water tables, and larger spacing between parallel trenches, (2) deeper or wider trenches do not substantially increase infiltration, (3) alternating wet/dry periods result in less overall infiltration than keeping the trenches continuously full, and (4) larger numbers of parallel trenches within a fixed area increases infiltration but with a diminishing effect as trench spacing becomes tighter. An empirical equation for estimating expected trench infiltration rates as a function of hydraulic conductivity and initial water-table depth was derived and can be used for evaluating feasibility of trench infiltration in other hydrogeologic settings. This article is protected by copyright. All rights reserved.

Description: In areas where peatlands are abundant, they are likely to play a significant role in the hydrological and hydrogeological dynamics of a watershed. Although individual case studies are reported in the literature, there is a large range of aquifer–peatland interactions and there is a need to understand the controls of these interactions. The objectives of this study were (1) to better understand aquifer–peatland connections and how these may be predicted by geology and geomorphic location and (2) to provide a variety of reference sites for glacial geological settings. Slope and depression peatlands were studied in the Abitibi-Témiscamingue region and in the St. Lawrence Lowlands, two contrasting regions of southern Quebec. A total of 12 transects that span a shallow aquifer–peatland interface were instrumented with piezometers. Field investigations included peatland characterization, monthly water level monitoring, and continuous hydraulic head measurements with pressure transducers. The results indicate that 7 of the 12 transects receive groundwater from the surrounding shallow aquifer. At the peatland margin, four lateral flow patterns were identified and associated with slope peatlands (parallel inflow and divergent flow) and with depression peatlands (convergent flow and parallel outflow). Vertical hydraulic gradients suggest that water flows mainly downwards, i.e. from the peatland to the underlying mineral deposits. Vertical connectivity appears to decrease as the distance from the peatland margin increases. All of these exchanges are important components in the sustainability of peatland hydrogeological functions. The regional comparison of aquifer–peatland flow dynamics performed in this study provides a new set of referenced data for the assessment of aquifer–peatland connectivity. Copyright © 2014 John Wiley & Sons, Ltd.

Description: In this study, we compare gridded snow depth estimates from the Snow Data Assimilation System (SNODAS) to snow depth observations derived from GPS Interferometric Reflectometry (GPS-IR) from roughly 100 Plate Boundary Observatory sites in the Western United States spanning four water-years (2010–2013). Data from these sites are not assimilated by SNODAS, thus GPS-IR measurements provide an independent data set to evaluate SNODAS. Our results indicate that at 80% of the sites, SNODAS and GPS-IR snow depth agree to better than 15-cm RMS error, with correlation coefficients greater than 0.6. Significant differences are found between GPS-IR and SNODAS for sites that are distant from other point measurements, are located in complex terrain, or are in areas with strong vegetation heterogeneities. GPS-IR estimates of snow depth are shown to provide useful error characterization of SNODAS products across much of the Western United States and may have potential as an additional data assimilation source that could help improve SNODAS estimates. This article is protected by copyright. All rights reserved.

Description: Prevention and mitigation of environmental disasters are affected by many factors, including perceptions and political risks (Dale et al., 1998; Neumayer et al., 2014). Individual perceptions are mostly influenced by memories. In the case of rare extreme events, they are therefore shaped to a large degree by inexperience. Institutional perceptions are often similarly shaped. This article is protected by copyright. All rights reserved.

Description: Soil CO 2 flux is strongly influenced by precipitation in many ecosystem types, yet knowledge of the effects of precipitation on soil CO 2 flux in semi-arid desert ecosystems remains insufficient, particularly for sandy soils. To address this, we investigated the response of sandy soil CO 2 flux to rainfall pulses in a desert ecosystem in northern China during August–September, 2011. Significant changes ( P  〈 0.05) were found in diel patterns of soil CO 2 flux induced by small (2.1 mm), moderate (12.4 mm) and large (19.7 mm) precipitation events. Further analysis indicated that rainfall pulses modified the response of soil CO 2 flux to soil temperature, including hysteresis between soil CO 2 flux and soil temperature, with F s higher when T s was increasing than when T s was decreasing, and the linear relationship between them. Moreover, our results showed that rainfall could result in absorption of atmospheric CO 2 by soil, possibly owing to mass flow of CO 2 induced by a gradient of gas pressure between atmosphere and soil. After each precipitation event, soil CO 2 flux recovered exponentially to pre-rainfall levels with time, with the recovery times exhibiting a positive correlation with precipitation amount. Based on the amounts of precipitation that occurred at our site during the measurement period (August–September), the accumulated rain-induced carbon absorption evaluated for rainy days was 1.068 g C m -2 ; this corresponds approximately to 0.5–2.1% of the net primary production of a typical desert ecosystem. Thus, our results suggest that rainfall pulses can strongly influence carbon fluxes in desert ecosystems. This article is protected by copyright. All rights reserved.

Description: Surface hydrological behaviour is important in drylands because it affects the distribution of soil moisture and vegetation and the hydrological functioning of slopes and catchments. Microplot scale runoff can be relatively easily measured, i.e. by rainfall simulations. However, slope or catchment runoff cannot be deduced from microplots, requiring long-time monitoring, because runoff coefficients decrease with increasing drainage area. Therefore, to determine the slope length covered by runoff ( runoff length ) is crucial to connect scales. Biological soil crusts (BSC) are good model systems and their hydrology at slope scale is insufficiently known. This study provides runoff lengths from BSCs, by field factorial experiments using rainfall simulation, including two BSC types, three rain types, three antecedent soil moistures and four plot lengths. Data were analysed by Generalized Linear Modeling, including vascular plant cover as covariates. Results were (i) the real contributing area is almost always much smaller than the topographical contributing area; (ii) the BSC type is key to controlling runoff; runoff length reached 3 m on cyanobacterial crust, but hardly over 1 m on lichen crust; this pattern remained through rain type or soil moisture; (iii) runoff decreased with BSC development because soil sealing disappears, porosity, biomass and roughness increase and some changes occur in the uppermost soil layer; (iv) runoff flow increased with both rain type and soil moisture, but runoff coefficient only with soil moisture (as larger rains increased both runoff and infiltration); vascular plant cover had a slight effect on runoff because it was low and random. This article is protected by copyright. All rights reserved.

Description: This study aimed to investigate the seasonal variability of runoff generation processes, the sources of stream water and the controls on the contribution of event water to streamflow for a small forested catchment in the Italian pre-Alps. Hydrometric, isotopic and electrical conductivity data collected between August 2012 and August 2013 revealed a marked seasonal variability in runoff responses. Noticeable differences in runoff coefficients and hydrological dynamics between summer and fall/spring rainfall events were related to antecedent moisture conditions and event size. Two- and three-component hydrograph separation and end-member mixing analysis showed an increase in event water contributions to streamflow with event size and average rainfall intensity. Event water fractions were larger during dry conditions in summer, suggesting that stormflow generation in summer consisted predominantly of direct channel precipitation and some saturated overland flow from the riparian zone. On the contrary, groundwater and hillslope soil water contributions dominated the streamflow response during wet conditions in fall. Seasonal differences were also noted between event water fractions computed based on isotopic and electrical conductivity data, likely due to the dilution effect during the wetter months. This article is protected by copyright. All rights reserved.

Description: Internal erosion in soils is characterized by a first step of detachment of solid particles from the granular skeleton under the action of a water seepage; then the detached particles are transported with the water flow. For some erosion processes, as suffusion, transported particles may finally be redeposited within the interstitial space of the soil itself acting as a filter. This paper focuses on the analysis and the description of the two first steps of particle detachment and transport in the cases of erosion by suffusion and piping erosion. The analysis is mainly based on direct numerical simulations performed with a fully coupled discrete element-lattice Boltzmann method (DE-LB method). Inter-particle interactions occurring in the solid granular phase are described with the discrete element method, whereas dynamics of the water flow is solved with the lattice Boltzmann method. Simulation results show that internal erosion of the solid phase can be described either from the hydraulic shear stress or from the power expended by the water seepage. The latter description based on the flow power is finally compared with experimental results from laboratory tests. Copyright © 2014 John Wiley & Sons, Ltd.

Description: Rain-induced erosion and short-term drought are the two factors that limit the productivity of croplands in the red soil region of subtropical China. The objective of this study was to estimate the effects of conservation practices on hydraulic properties and root zone water dynamics of the soil. A three-year experiment was performed on a slope at Xianning. Four treatments were evaluated for their ability to reduce soil erosion and improve soil water conditions. Compared to no-practices (CK) and living grass strips (GS), the application of polyacrylamide (PAM) significantly reduced soil crust formation during intense rainfall, while rice straw mulching (SM) completely abolished soil crust formation. The SM and PAM treatments improved soil water stable aggregates, with a redistribution of micro-aggregates into macro-aggregates. PAM and SM significantly increased the soil water-holding capacity. These practices mitigated the degradation of the soil saturated hydraulic conductivity (Ks) during intense rainfalls. These methods increased soil water storage but with limited effects during heavy rainfalls in the wet period. In contrast, during the dry period, SM had the highest soil water storage, followed by PAM and CK. Grass strips had the lowest soil water storage because of the water uptake during the vigorous grass growth. A slight decline in the soil moisture resulted in a significant decrease in the unsaturated hydraulic conductivity (Ku) of the topsoil. Therefore, the hydraulic conductivity in the field is governed by soil moisture, and the remaining soil moisture is more important than improving soil properties to resist short-term droughts. As a result, SM is the most effective management practice when compared to PAM and GS, although they all protect the soil hydraulic properties during wet periods. These results suggest that mulching is the best strategy for water management in erosion- and drought-threatened red soils. This article is protected by copyright. All rights reserved.

Description: The distribution of streamwater within ice-covered lakes influences sub-ice currents, biological activity, and shoreline morphology. Perennially ice-covered lakes in the McMurdo Dry Valleys, Antarctica, provide an excellent natural laboratory to study hydrologic-limnologic interactions under ice cover. For a two-hour period on 17 December 2012, we injected a lithium chloride tracer into Andersen Creek, a pro-glacial stream flowing into Lake Hoare. Over four hours, we collected 182 water samples from five stream sites and fifteen ice boreholes. Geochemical data showed that interflow traveled West of the stream mouth along the shoreline, and did not flow towards the lake interior. The chemistry of water from Andersen Creek was similar to the chemistry of water below shoreline ice. Additional evidence for Westward flow included the morphology of channels on the ice surface, the orientation of ripple marks in lake sediments at the stream mouth, and equivalent temperatures between Andersen Creek and water below shoreline ice. Streamwater deflected to the right of the mouth of the stream, in the opposite direction predicted by the Coriolis force. Deflection of interflow was probably caused by the diurnal addition of glacial runoff and stream discharge to the Eastern edge of the lake which created a strong pressure gradient sloping to the West. This flow directed stream momentum away from the lake interior, minimizing the impact of stream momentum on sub-ice currents. It also transported dissolved nutrients and suspended sediments to the shoreline region instead of the lake interior, potentially affecting biological productivity and bedform development. This article is protected by copyright. All rights reserved.

Description: Most runoff analyses using a grid-based distributed model use one parameter group calibrated at the outlet of a watershed, instead of dividing the watershed into subwatersheds. Significant differences between the observed value and the simulation result of the subwatersheds can occur if just one parameter group is used in all subwatersheds that have different hydrological characteristics from each other. Therefore, to improve the simulation results of the subwatersheds within a watershed, a model calibrated at every subwatershed needs to be used to reflect the characteristics of each subwatershed. In this study, different parameter groups were set up for one or two sites using a distributed model, the GRM (Grid based Rainfall-runoff Model), and the evaluations were based on the results of rainfall-runoff analysis, which uses a multi-site calibration (MSC) technique to calibrate the model at the outlet of each site. The Hyangseok watershed in Naeseong River, which is a tributary of Nakdong River in Korea, was chosen as the study area. The watershed was divided into 5 subwatersheds each with a subwatershed outlet that was applied to the calibration sites. The MSC was applied for 5 cases. When a site was added for calibration in a watershed, the runoff simulation showed better results than the calibration of only one site at the most downstream area of the watershed. The MSC approach could improve the simulation results on the calibrated sites and even on the non-calibrated sites, and the effects of MSC improved when the calibrated site was closer to the runoff site. This article is protected by copyright. All rights reserved.

Description: Studies quantifying evaporation from permeable pavement systems are limited to a few laboratory studies and one field application. This research quantifies evaporation for a larger field application by measuring the water balance from lined permeable pavement sections. The U.S. Environmental Protection Agency constructed a 0.4-ha parking lot in Edison, NJ, that incorporated three different permeable pavement types in the parking lanes – permeable interlocking concrete pavers (PICP), pervious concrete (PC), and porous asphalt (PA). An impermeable liner installed 0.4 m below the surface in four 11.6-m by 4.74-m sections per each pavement type captures all infiltrating water and routes it to collection tanks that can contain events up to 38 mm. Each section has a design impervious area to permeable pavement area ratio of 0.66:1. Pressure transducers installed in the underdrain collection tanks measured water level for 24 months. Level was converted to volume using depth-to-volume ratios for individual collection tanks. Using a water balance approach, the measured infiltrate volume was compared to rainfall volume on an event-basis to determine the rainfall retained in the pavement strata and underlying aggregate. Inter-event evaporation created additional storage in the pavement and aggregate layers. Events were divided into three groups based on antecedent dry period (ADP) and three, four-month groups of potential evaporation based on historical monthly pan evaporation records. There was a significant difference in rainfall retained among the various combinations of ADP and potential evaporation groups. More rainfall was retained in the pavement and aggregate layers as time between events increased and during warmer months with larger potential evaporation. Average cumulative evaporation from the permeable pavement sections for 134 rainfall events in 24 months was 5.2% of the cumulative rainfall volume, and the range was 2.4–7.6%. Each PC section had more annual evaporation than any individual PICP or PA section. While measureable, evaporation is a small contribution to the total water budget on an annual basis for these systems. This article is protected by copyright. All rights reserved.

Description: Stationarity is often assumed for frequency analysis of low flows in water resources management and planning. However, many studies have shown that flow characteristics, particularly the frequency spectrum of extreme hydrologic events, were modified by climate change and human activities. Thus the conventional frequency analysis which fails to consider the nonstationary characteristics may lead to costly design. The analysis presented in this paper was based on the more than 100 years of daily flow data from the Yichang gaging station 44 kilometers downstream of the Three Gorges Dam. The Mann-Kendall trend test under the scaling hypothesis showed that the annual low flows had a significant monotonic trend, whereas an abrupt change point was identified in 1936 by the Pettitt test. The climate-informed low flow frequency analysis and the divided and combined method were employed to account for the impacts from related climate variables and nonstationarities in annual low flows. Without prior knowledge of the probability density function for the gaging station, six distribution functions including the Generalized Extreme Values (GEV), Pearson Type III, Gumbel, Gamma, Lognormal, and Weibull distributions have been tested to find the best fit, in which the local likelihood method is used to estimate the parameters. Analyses show that GEV had the best fit for the observed low flows. This study has also shown that the climate-informed low flow frequency analysis is able to exploit the link between climate indices and low flows, which would account for the dynamic feature for reservoir management and provide more accurate and reliable designs for infrastructure and water supply. This article is protected by copyright. All rights reserved.

Description: Saltwater intrusion problems have been usually tackled through analytical models because of its simplicity, easy implementation and low computational cost. Most of these models are based on the sharp-interface approximation and the Ghyben-Herzberg relation, which neglects mixing of fresh water and seawater and implicitly assumes that salt water remains static. This paper provides insight into the validity of a sharp-interface approximation defined from a steady state solution when applied to transient seawater intrusion problems (SWI). The validation tests have been performed on a 3D unconfined synthetic aquifer, which include spatial and temporal distribution of recharge and pumping wells. Using a change of variable the governing equation of the steady state sharp-interface problem can be written with the same structure of the steady confined groundwater flow equation as a function of a single potential variable (ϕ). We propose to approach also the transient problem solving a single potential equation (using also the ϕ variable) with the same structure of the confined groundwater flow equation. It will allow solving the problem by using the classical MODFLOW code. We have used the parameter estimation model PEST to calibrate the parameters of the transient sharp-interface equation. We show how after the calibration process the sharp-interface approach may provide accurate enough results when applied to transient problems and improve the steady state results, thus avoiding the need of implementing a density-dependent model and reducing the computational cost. This has been proved by comparing results with those obtained using the finite difference numerical code SEAWAT for solving the coupled partial differential equations of flow and density-dependent transport. The comparison was performed in terms of piezometric heads, seawater penetration, transition zone width and critical pumping rates. This article is protected by copyright. All rights reserved.

Description: Pan evaporation (E p ) is an important indicator of water and energy and the decline of E p has been reported in many regions over the last decades. The climate and E p are dependent on each other. In this study, the temporal trends of E p and main E p drivers, namely mean air temperature (Ta), wind speed ( u ), global solar radiation (Rs), net long-wave radiation(R nl ) and vapour pressure deficit (D) from 1970 to 2012, were calculated based on 26 meteorological stations on the Tibetan Plateau(TP). The arithmetic average of E p from 26 stations decreased with the rate of −11.91 mm a −2 ; the trends of R s , R nl , T a , u and D were −1.434w m −2 decade −1 , 0.2511 w m −2 decade −1 , 0.3590°Cdecade −1 , −0.2376 m s −1 decade −1 and 9.523 Pa decade −1 respectively. The diffuse irradiance is an essential parameter to model E p and quantify the contribution of climatic factors to changing E p . 60724 observations of R s and diffuse solar irradiance (R d ) from 7 of the 26 stations were used to develop the correlation between the diffuse fraction (R d /R s ) and the clearness index (R s /R o ). Based on the estimation of the diffuse component of R s and climatic data, we modified the PenPan model to estimate Chinese micro-pan evaporation (E p ) and assess the attribution of E p dynamics using partial derivatives. The results showed that there was a good agreement between the observed and calculated daily E p values. The observed decrease in E p was mostly due to declining wind speed (−13.7 mm a −2 ) with some contributions from decreasing solar irradiance (−3.1 mm a −2 ); and the increase of temperature had a large positive effect (4.55 mm a −2 ) in total while the increase of R nl had insignificant effect (0.35 mm a −2 ) on E p rates. The change of E p is the net result of all the climatic variables. This article is protected by copyright. All rights reserved.

Description: The recharge processes have been evaluated for two karst massifs of southern Italy, the Mt. Terminio and Mt. Cervialto, characterized by wide endorheic areas. The annual means recharge has been estimated by GIS tools, from regression of annual mean values of different ground-elevated rain gauges and thermometers. The recharge has been distinguished for endorheic areas and the other areas of springs catchment, and the ratio between the output spring and input rainfall has been also estimated (recharge coefficient). The annual recharge has been used to calibrate a daily scale model, which allows to estimate the amount of effective rainfall which is retained as soil moisture, the amount reaching the water table (recharge s.s.), and the amount of rainfall which develops the runoff. All this amounts vary through the hydrological year, in function of soil moisture deficit and daily rainfall intensity. The model allows estimating the recharge conditions through the hydrological year, and it is a useful tool for water management. This article is protected by copyright. All rights reserved.

Description: Stream water temperature ( t s ) is a critical water quality parameter for aquatic ecosystems. However, t s records are sparse or nonexistent in many river systems. In this work, we present an empirical model to predict t s at the site scale across the U.S. The model, derived using data from 171 reference sites selected from the Geospatial Attributes of Gages for Evaluating Streamflow (GAGES) database, describes the linear relationship between monthly-mean air temperature ( t a ) and t s . Multiple linear regression models are used to predict the slope ( m ) and intercept ( b ) of the t a -t s linear relation as a function of climatic, hydrologic, and land cover characteristics. Model performance to predict t s resulted in a mean Nash-Sutcliffe (NS) efficiency coefficient of 0.78 across all sites. Application of the model to predict t s at additional 89 non-reference sites with a higher human alteration yielded a mean NS value of 0.45. We also analyzed seasonal thermal sensitivity ( m ) and found strong hysteresis in the t a -t s relation. Drainage area exerts a strong control on m in all seasons, whereas the cooling effect of groundwater was only evident for the spring and fall seasons. However groundwater contributions are negatively related to mean t s in all seasons. Finally we found that elevation and mean basin slope are negatively related to mean t s in all seasons, indicating that steep basins tend to stay cooler due to shorter residence times to gain heat from their surroundings. This model can potentially be used to predict climate change impacts on t s across the U.S. This article is protected by copyright. All rights reserved.

Description: Assessment of potential climate change impacts on stream water temperature (T s ) across large scales remains challenging for resource managers because energy exchange processes between the atmosphere and the stream environment are complex and uncertain, and few long-term datasets are available to evaluate changes over time. In this study, we demonstrate how simple monthly linear regression models based on short-term historical T s observations and readily available interpolated air temperature (T a ) estimates can be used for rapid assessment of historical and future changes in T s . Models were developed for 61 sites in the southeastern U.S. using ≥18 months of observations, and were validated at sites with longer periods of record. The T s models were then used to estimate temporal changes in T s at each site using both historical estimates and future T a projections. Results suggested that the linear regression models adequately explained the variability in T s across sites and the relationships between T s and T a remained consistent over as many as 37 years. We estimated that most sites had increases in historical annual mean T s between 1961 and 2010 (mean +0.11 °C decade −1 ). All 61 sites were projected to experience increases in T s from 2011 to 2060 under the three climate projections evaluated (mean +0.41 °C decade −1 ). Several of the sites with the largest historical and future T s changes were located in ecoregions home to temperature-sensitive fish species. This methodology can be used by resource managers for rapid assessment of potential climate change impacts on stream water temperature. This article is protected by copyright. All rights reserved.

Description: Overflow-driven lateral connectivity significantly influences the spatial distribution and diversity of floodplain habitats and biota. Proper understanding of lateral connectivity in floodplain and backwater channels is therefore critical for assessment of river quality and for targeting management or restoration actions. In this study, we present a methodological framework for spatial and temporal assessment of overflow-driven lateral connectivity at two spatial scales; by-pass reach and backwater channel. Firstly, we compute the relative elevations, as well as overflow discharge, duration, and frequency using a simple, raster-based method that uses a LiDAR Digital Elevation Model (DEM), rating curves, and stream flow time series. Subsequently, we analyse the accuracy of this approach with respect to the accuracy of a DEM and evaluate its further applications. Altogether, four, 10-kilometer-long by-pass reaches and eleven backwater channels are analysed, located along the Rhône River corridor in France. The results proved the precision of the method to be affected by the LiDAR DEM accuracy, which was on average more precise in a typically homogeneous floodplain setting rather than for backwater channel plugs with pronounced topographic complexity and usually riparian forest canopy. Amongst the 4 studied reaches, Brégnier Cordon proved to have the greatest flooding dynamics, followed by Belley and Chautagne. The hydrological connectivity pattern of Pierre Bénite differed significantly. Three longitudinal patterns of hydrological connectivity of backwater channels displayed stepwise advancement of the water. The presented results can be used to assess ecological potential of floodplain habitats and their historic and prospective evolution through time. This article is protected by copyright. All rights reserved.

Description: Lag times in reduced nutrient leaching after improved agricultural practices must be assessed to inform management decisions and evaluate their cost-effectiveness. This study estimated the leaching of phosphorus (P) and nitrogen (N) at two scales, a 33.8-ha nested field (data from 1973-2011) and an 820-ha agricultural catchment (data from 1992-2010). Field management was evaluated along with long-term nutrient trends. Estimates including and excluding nutrient concentrations in the stream under dry catchment conditions (mean 2.5 months yr -1 ) revealed that wastewater contributed 10% of total P (TP) catchment leaching, mostly in dissolved reactive (DRP) form. More recent flow-proportional sampling at the two scales demonstrated 45% higher particulate P leaching from the field than with discrete water sampling, while a past discrete sampling strategy may have overestimated DRP contributions to the stream. The accumulated field P balance was increasingly negative after 1987, whereas crop yields increased. From 1998, the measured accumulated TP leaching from the field was lower than the mean accumulated leaching, considering the estimated downward trend (-10%) over the 38-year study period (p 〈0.05). The average total nitrogen (TN) field leaching of 28 kg ha -1  yr -1 (1973-2011) was 10% higher than the catchment leaching (1992-2010). The rates and timing of field N and P fertilisation became better adapted to crop requirements over time, and thereafter, a 14% reduction in TN leaching was estimated. No significant trends were estimated for catchment leaching for either TP or TN over the 18-year-period, demonstrating an extended lag period for reduced nutrient leaching and the need for long-term monitoring of the effects of pollution mitigation. This article is protected by copyright. All rights reserved.

Description: There is global concern about headwater management and associated impacts on river flow. In many wet temperate zones peatlands can be found covering headwater catchments. In the UK there is major concern about how environmental change, driven by human interventions, has altered the surface cover of headwater blanket peatlands. However, the impact of such land-cover changes on river flow is poorly understood. In particular, there is poor understanding of the impacts of different spatial configurations of bare peat or well-vegetated, restored peat on river flow peaks in upland catchments. In this paper, a physically-based, distributed and continuous catchment hydrological model was developed to explore such impacts. The original TOPMODEL, with its process representation being suitable for blanket peat catchments, was utilized as a prototype acting as the basis for the new model. The equations were downscaled from the catchment level to the cell level. The runoff produced by each cell is divided into subsurface flow and saturation-excess overland flow before an overland flow calculation takes place. A new overland flow module with a set of detailed stochastic algorithms representing overland flow routing and re-infiltration mechanisms was created to simulate saturation-excess overland flow movement. The new model was tested in the Trout Beck catchment of the North Pennines of England and found to work well in this catchment. The influence of land cover on surface roughness could be explicitly represented in the model and the model was found to be sensitive to land cover. This article is protected by copyright. All rights reserved.

Description: We examine how tracer studies have enhanced our understanding of flow paths, residence times and sources of stream flow in northern catchments. We define northern catchments as non-glacial sites in the temperate conifer/boreal/permafrost zone, focussing our review mainly on sites in North America and Europe. Improved empirical and theoretical understanding of hydrological functioning has advanced the analytical tools available for tracer-based hydrograph separations, derivation of transit time distributions and tracer-aided rainfall-runoff models that are better able to link hydrological response to storage changes. However, the lack of comprehensive tracer data sets still hinders development of a generalized understanding of how northern catchments will respond to change. This paucity of empirical data leads to many outstanding research needs, particularly in rapidly changing areas that are already responding to climatic warming and economic development. To continually improve our understanding of hydrological processes in these regions our knowledge needs to be advanced using a range of techniques and approaches. Recent technological developments for improved monitoring, distributed hydrological sensor systems, more economic analysis of large sample numbers in conjunction with novel, tracer-aided modelling approaches and the use of remote sensing have the potential to help understanding of northern hydrological systems as well as inform policy at a time of rapid environmental change. This article is protected by copyright. All rights reserved.